Travel from a 58-degree cave in Mexico to the diamond pipes of South Africa and the mines of Hunan. On the way, collect 100 technical English words, learn how crystals really grow, and finish by making your own video that teaches other people about your crystals.
这是一份为期约两周的英语趣味“家庭课堂”，主题是水晶与矿物。孩子在轻松有趣的探索中，继续练习学术和科技英语，不需要家长额外辅导。
页面不含任何姓名或个人信息，不需要注册，也没有广告。这只是一个轻松、有趣的方式，让英语不断线。
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Each day is 15 to 20 minutes: one word set of 10 words plus one or two short tasks. You can do it in any order, but the order below works well. Tick each day when you are done.
Tip: say every word out loud twice. Hearing yourself helps you remember.
Ten sets of ten. Each word has the IPA, a pronunciation respelling (capital letters are the stressed syllable), a precise definition, an example sentence, a word family or collocations, and an optional Chinese hint. Press the speaker to listen. Tick “I can use it” when you can say it in a sentence of your own.
Audio is not available in this browser. Use the IPA and the respelling (for example LAT-iss) instead, or open the page in Safari or Chrome.
The printable A4 sheet of all 100 words (with a blank practice column) is here: crystal-hunter-100-words.pdf.
The repeating, three-dimensional pattern in which the atoms or ions inside a crystal are arranged.
“Table salt forms little cubes because its atoms sit in a cubic lattice.”
Word family / collocations: crystal lattice; lattice structure; a regular lattice
晶格The smallest block of a lattice that, when copied over and over in every direction, builds the whole crystal.
“The simplest unit cell is a cube with one atom at each corner.”
Word family / collocations: cubic unit cell; unit cell dimensions; repeat the unit cell
晶胞The first step of crystal growth, when a few particles clump together into a tiny seed that is stable enough to keep growing.
“A speck of dust in the solution can trigger nucleation.”
Word family / collocations: nucleate (verb); nucleus (noun); nucleation site
成核（晶核形成）The state of a solution that holds more dissolved material than it normally could at that temperature. It is unstable, so crystals tend to appear.
“Cooling the hot solution creates supersaturation, so crystals start to grow.”
Word family / collocations: supersaturated solution; saturated (adjective); saturate (verb)
过饱和The typical overall shape that a crystal takes as it grows.
“Quartz usually has a prismatic habit, like a six-sided pencil with a point.”
Word family / collocations: crystal habit; prismatic, tabular or needle-like habit
晶习（晶体常见形态）The growth of two or more crystals joined together in a regular, symmetrical way, as if one were a mirror image of the other.
“Twinning gives the mineral staurolite its famous cross shape.”
Word family / collocations: twin (noun, verb); twinned crystal; contact twin
孪晶（双晶）One of two or more minerals that have the same chemical formula but different crystal structures.
“Diamond is a polymorph of carbon, and so is graphite.”
Word family / collocations: polymorphic (adjective); polymorphism; polymorph of calcite
同质多象变体A balanced, regular pattern. A crystal has symmetry if it looks the same after being rotated or reflected.
“A snowflake has six-fold symmetry: turn it by 60 degrees and it looks the same.”
Word family / collocations: axis of symmetry; rotational symmetry; symmetrical (adjective)
对称One flat, smooth surface (a face) on a crystal or on a cut gem.
“Light flashes from every facet as you turn the crystal.”
Word family / collocations: crystal face; faceted gem; multi-faceted
晶面；刻面Having no regular internal pattern of atoms, so not crystalline.
“Glass is amorphous, which is why it has no natural crystal faces.”
Word family / collocations: amorphous solid; amorphous silica; crystalline (opposite)
非晶质的6 questions: 3 multiple choice and 3 typed. Score 5 or more to earn 5 points.
The way light reflects from the surface of a mineral, for example metallic, glassy, silky or dull.
“Pyrite has a metallic luster, but quartz has a glassy luster.”
Word family / collocations: metallic luster; vitreous (glassy) luster; lustrous (adjective)
光泽How well a mineral resists being scratched. Geologists measure it with the Mohs scale.
“Quartz has a hardness of 7, so a steel knife cannot scratch it.”
Word family / collocations: Mohs hardness; test the hardness; hard, harder, hardest
硬度A ranking from 1 to 10 of minerals by which one can scratch which, from talc (1) to diamond (10).
“On the Mohs scale, fluorite (4) can scratch calcite (3) but not quartz (7).”
Word family / collocations: Mohs hardness; scratch test; named after Friedrich Mohs
莫氏硬度表The tendency of a mineral to break along flat, smooth planes because its atomic bonds are weaker in those directions.
“Calcite has perfect cleavage, so it splits into small slanted blocks.”
Word family / collocations: perfect, good or poor cleavage; cleavage plane; cleave (verb)
解理The way a mineral breaks when it does not split along cleavage planes. A curved, shell-like break is called conchoidal.
“Quartz has no cleavage, so it breaks with a curved, conchoidal fracture.”
Word family / collocations: conchoidal fracture; uneven fracture; fracture (verb)
断口The color of a mineral's powder when it is rubbed on an unglazed white tile. It is often more reliable than the color of the crystal.
“Hematite can look silver or black, but its streak is always reddish-brown.”
Word family / collocations: streak plate; streak test; streak color
条痕The density of a material divided by the density of water. It has no units and shows how heavy a mineral feels for its size.
“Quartz has a specific gravity of about 2.65, so it weighs 2.65 times as much as the same volume of water.”
Word family / collocations: relative density; heavy for its size; measure the specific gravity
比重（相对密度）The bending of light when it passes from one material into another, such as from air into a crystal.
“Diamond bends light so strongly that refraction makes it sparkle.”
Word family / collocations: refractive index; refract (verb); angle of refraction
折射The splitting of one ray of light into two rays that travel at different speeds inside certain crystals.
“Through a clear piece of calcite, a line of writing looks doubled because of birefringence.”
Word family / collocations: birefringent (adjective); double refraction; Iceland spar
双折射Letting some light pass through, but scattering it so that you cannot see a clear picture through the material.
“Milky quartz is translucent, like frosted glass.”
Word family / collocations: transparent, translucent, opaque; translucency
半透明的6 questions: 3 multiple choice and 3 typed. Score 5 or more to earn 5 points.
A naturally occurring, solid, non-living substance with a definite chemical makeup and an orderly crystal structure.
“Quartz is a mineral, but steel is not, because people make steel.”
Word family / collocations: mineral species; mineralogy; mineralogist
矿物A mineral built from silicon and oxygen, usually combined with other elements. Silicates are the most common minerals in Earth's crust.
“Quartz is a silicate, and so are feldspar and mica.”
Word family / collocations: silicate mineral; silica; silicon
硅酸盐A mineral that contains carbon and oxygen bonded together as the carbonate group.
“Calcite is a carbonate, and it fizzes in weak acid.”
Word family / collocations: calcium carbonate; carbonate rock; limestone
碳酸盐A mineral in which a metal is combined with sulfur. Many sulfides are important metal ores.
“Pyrite, nicknamed fool's gold, is an iron sulfide.”
Word family / collocations: sulfide ore; sulfide mineral; sulfur
硫化物A mineral in which a metal is combined with oxygen.
“Hematite is an iron oxide, and corundum, which includes ruby and sapphire, is aluminum oxide.”
Word family / collocations: iron oxide; oxidize (verb); oxidation
氧化物An element that is found in nature in its pure form, not combined with other elements.
“Gold is a native element, and so are copper, sulfur and diamond (pure carbon).”
Word family / collocations: native gold; native copper; element
自然元素A tiny amount of foreign atoms inside a crystal. Impurities often change a crystal's color.
“A little chromium as an impurity makes corundum red, and then we call it ruby.”
Word family / collocations: trace impurities; pure, impure; purity
杂质An element that is present in only very small amounts in a mineral, often much less than one percent.
“Iron, present as a trace element, helps give amethyst its purple color.”
Word family / collocations: trace amounts; trace chemistry; trace (verb)
微量元素A bit of another mineral, a liquid or a gas that was trapped inside a crystal while it was growing.
“The thin golden needle of rutile inside the quartz is an inclusion.”
Word family / collocations: fluid inclusion; mineral inclusion; include (verb)
包裹体The glow that some minerals give off while ultraviolet light shines on them. It stops when the light is switched off.
“Under UV light, some fluorite glows blue, and the word fluorescence comes from fluorite.”
Word family / collocations: fluorescent (adjective); ultraviolet (UV) light; phosphorescence
荧光6 questions: 3 multiple choice and 3 typed. Score 5 or more to earn 5 points.
Hot, molten rock under Earth's surface. It holds dissolved gases and sometimes small crystals.
“When magma cools slowly underground, large crystals can grow.”
Word family / collocations: magma chamber; magma cools; lava (magma that erupts)
岩浆Describes rock that formed when magma or lava cooled and hardened.
“Granite is an igneous rock, and you can see its quartz and feldspar crystals.”
Word family / collocations: igneous rock; intrusive and extrusive igneous rocks
火成的Describes rock that was changed by heat and pressure deep underground, without melting completely.
“Limestone turns into marble, a metamorphic rock, when it is heated and squeezed.”
Word family / collocations: metamorphic rock; metamorphism; metamorphose (verb)
变质的Describes rock made from layers of sand, mud, shells or dissolved minerals that were pressed together over a long time.
“The Herkimer crystals grew in a sedimentary rock called dolostone.”
Word family / collocations: sedimentary rock; sediment; layers (strata)
沉积的A very coarse-grained igneous rock with huge crystals, formed from the last, water-rich part of a cooling magma.
“A pegmatite is famous for big crystals of tourmaline, topaz and mica.”
Word family / collocations: pegmatite dike; granite pegmatite; gem pegmatite
伟晶岩A crack in rock that was filled with minerals which crystallized from hot, mineral-rich water.
“Many quartz crystals in Arkansas grew in a hydrothermal vein.”
Word family / collocations: hydrothermal fluid; quartz vein; vein (noun)
热液脉A roughly round rock with a hollow center that is lined with crystals.
“We cracked open the geode and found a sparkling cave of purple amethyst.”
Word family / collocations: amethyst geode; crack open a geode
晶腺（晶洞）A small cavity in a rock, often lined with crystals.
“The miner split the dolostone and found a vug full of clear quartz crystals.”
Word family / collocations: vuggy (adjective); a vug lined with crystals; cavity
岩石中的空洞（晶洞）A crust of tiny crystals covering a rock surface or the inside of a cavity.
“The inside of the geode was a glittering druse of quartz.”
Word family / collocations: drusy quartz; druzy (jewelry spelling); crystal crust
晶簇（细小晶体形成的晶壳）A mineral or rock left behind when salty water evaporates.
“Halite, or rock salt, is an evaporite, and so is gypsum.”
Word family / collocations: evaporite deposit; evaporate (verb); evaporation
蒸发岩6 questions: 3 multiple choice and 3 typed. Score 5 or more to earn 5 points.
A rock from explosive volcanic eruptions that carries diamonds up from deep inside Earth. It is found in carrot-shaped pipes.
“Most diamond mines follow a pipe of kimberlite down into the ground.”
Word family / collocations: kimberlite pipe; named after Kimberley, South Africa
金伯利岩The thin, solid outer layer of Earth, made of rock.
“The crust is roughly 30 to 50 kilometers thick under the continents.”
Word family / collocations: Earth's crust; continental crust; oceanic crust
地壳The thick layer of hot, slowly flowing rock between Earth's crust and its core.
“Natural diamonds form deep in the mantle, at least 150 kilometers down.”
Word family / collocations: upper mantle; mantle rock; mantle plume
地幔The theory that Earth's outer shell is broken into giant plates that move slowly, building mountains and causing earthquakes.
“Plate tectonics lifted the Alps when the African and European plates collided.”
Word family / collocations: tectonic plate; plate boundary; collision
板块构造The slow breakdown of rock at Earth's surface by rain, wind, ice and chemicals.
“Weathering slowly freed the quartz crystals from the crumbling rock.”
Word family / collocations: chemical weathering; physical weathering; weathered rock
风化The movement of weathered rock and soil by water, wind or ice.
“Erosion exposed the pegmatite on the side of the hill.”
Word family / collocations: soil erosion; erode (verb); river erosion
侵蚀Rock that contains enough of a valuable metal or mineral that it is worth mining.
“Wolframite is an ore of tungsten.”
Word family / collocations: iron ore; ore body; smelt the ore
矿石A natural concentration of a mineral or ore in one place.
“The mine sits on a rich diamond deposit.”
Word family / collocations: mineral deposit; ore deposit; deposit (verb): to lay down
矿床A long, narrow crack in rock.
“In the Alps, quartz crystals grew inside a fissure opened up by mountain building.”
Word family / collocations: alpine fissure; fissure vein; fissured rock
裂隙The rock that surrounds and contains a vein, cavity or ore deposit.
“The host rock at Herkimer is a Cambrian dolostone.”
Word family / collocations: host rock; surrounding rock; country rock
围岩（主岩）6 questions: 3 multiple choice and 3 typed. Score 5 or more to earn 5 points.
A mineral, or sometimes a rock or organic material, that is cut and polished for jewelry because it is beautiful, durable and rare.
“Ruby is a gemstone, and its mineral name is corundum.”
Word family / collocations: precious gemstone; gem-quality; semi-precious
宝石A unit of mass for gemstones. One carat equals 0.2 grams.
“One carat is just 0.2 grams, so a ten-carat diamond weighs only two grams.”
Word family / collocations: carat weight; a two-carat diamond; not the same as karat (gold purity)
克拉How free a gem is from inclusions and surface flaws.
“A gem with no visible inclusions has high clarity.”
Word family / collocations: clarity grade; flawless; clear (adjective)
净度A gem that is polished into a smooth, rounded dome instead of being cut with facets.
“An opal is often cut as a cabochon to show off its colors.”
Word family / collocations: cabochon cut; domed; polished
弧面型宝石Natural and uncut; not yet shaped or polished. Gem dealers also use it as a noun.
“He bought a piece of rough ruby and had it cut into a gem.”
Word family / collocations: rough diamond; rough stone; polished (opposite)
未加工的（原石）The craft of cutting and polishing stones, or a person who does this work.
“A skilled lapidary turned the rough tourmaline into a glowing gem.”
Word family / collocations: lapidary workshop; lapidary artist; lapidary wheel
宝石切磨工艺（工匠）Made by people in a lab or factory, but with the same chemistry and structure as the natural mineral.
“Synthetic quartz is grown in factories and used in watches and electronics.”
Word family / collocations: synthetic gem; lab-grown; natural versus synthetic
合成的A sample of a mineral that is kept for study, display or collecting.
“The museum's best azurite specimen came from Tsumeb.”
Word family / collocations: mineral specimen; museum-quality specimen; collect a specimen
标本The record of where a specimen or gem came from and who has owned it.
“A crystal with clear provenance is worth more to collectors.”
Word family / collocations: trace the provenance; provenance records; origin
来源与流转记录Heating a gem to improve its color or clarity.
“Many sapphires on the market have had heat treatment.”
Word family / collocations: heat-treated stone; untreated (natural); enhancement
热处理6 questions: 3 multiple choice and 3 typed. Score 5 or more to earn 5 points.
A hammer with a flat face on one side and a pick or chisel tip on the other, used for breaking rock.
“Always wear safety glasses when you swing a rock hammer.”
Word family / collocations: geologist's hammer; hammer and chisel; swing a hammer
地质锤A metal tool with a sharp, flat edge that you tap with a hammer to split rock along a crack.
“Tap the chisel gently along the seam.”
Word family / collocations: cold chisel; hammer and chisel; chisel away
凿子A small magnifying lens, often 10 times magnification, used to study crystals closely.
“Through the loupe, I could see tiny inclusions inside the crystal.”
Word family / collocations: 10x loupe; hand lens; jeweler's loupe
放大镜（珠宝放大镜）Searching an area for useful minerals, metals or gems.
“While prospecting in the creek, she found quartz pebbles that led her up the hill.”
Word family / collocations: prospector; prospect (verb); go prospecting
找矿（勘探）A place where bedrock sticks out above the soil so that geologists can see and study it.
“We studied the pegmatite outcrop beside the road.”
Word family / collocations: rock outcrop; exposed outcrop; crop out (verb)
露头Loose pieces of rock or crystal that have broken off bedrock and lie on the ground, away from where they came from.
“Finding quartz float told us to search uphill for the vein.”
Word family / collocations: follow the float; float trail; float (verb)
转石（浮石）The leftover rock and waste dumped after the valuable minerals have been taken out of ore.
“Visitors often hunt for crystals in the mine's tailings.”
Word family / collocations: tailings pile; tailings dump; sort through tailings
尾矿A piece of land where a person or company has the legal right to mine minerals.
“Do not dig on a mining claim without the owner's permission.”
Word family / collocations: mining claim; stake a claim; claim owner
采矿权地块An official written permission to collect, dig or enter an area.
“In some protected areas you need a permit before you can collect even one stone.”
Word family / collocations: collecting permit; apply for a permit; permit (verb, pur-MIT)
许可证The exact place where a mineral specimen was found.
“Always write the locality on the label of your specimen.”
Word family / collocations: type locality; locality data; local (adjective)
产地6 questions: 3 multiple choice and 3 typed. Score 5 or more to earn 5 points.
An open pit where stone is cut or blasted out of the ground.
“The crystals were found in a limestone quarry.”
Word family / collocations: stone quarry; quarry face; quarry (verb)
采石场A vertical or steeply sloping tunnel in a mine.
“A lift carried the miners down the shaft.”
Word family / collocations: mine shaft; sink a shaft; ventilation shaft
竖井A horizontal tunnel that enters a mine from the side of a hill.
“The old adit was sealed to keep hikers out.”
Word family / collocations: abandoned adit; adit entrance; drive an adit
平硐A cavity in a vein or rock that is filled with crystals. Collectors use this word for a crystal-filled cavity.
“The crew hit a pocket of tourmaline crystals.”
Word family / collocations: crystal pocket; strike a pocket; gem pocket
晶囊（含晶体的空洞）The soil and rock that lie on top of a mineral deposit and must be removed to reach it.
“Miners strip the overburden before they reach the pegmatite.”
Word family / collocations: remove the overburden; overburden removal; burden
覆盖层（剥离层）Using explosives to break rock. Only trained professionals do this.
“Blasting can shatter crystals, so careful miners switch to hand tools near a pocket.”
Word family / collocations: blast (verb, noun); blasting crew; controlled blast
爆破A deposit of heavy, valuable minerals such as gold or gems that moving water has concentrated in sand and gravel.
“Rubies and gold can collect in a river placer.”
Word family / collocations: placer deposit; placer mining; placer gold
砂矿Carried and left behind by flowing water, such as river sand and gravel.
“Rubies near Mogok are mined from alluvial gravel.”
Word family / collocations: alluvial gravel; alluvial fan; alluvium
冲积的Shaking or washing material through a mesh to separate big pieces from small ones.
“Screening the gravel in water makes the sparkly crystals easy to spot.”
Word family / collocations: screen (noun, verb); wet screening; sieve
筛选A sloping water channel used to wash gravel so that heavier minerals settle and lighter mud washes away.
“A sluice uses flowing water to carry mud away and leave heavy crystals behind.”
Word family / collocations: sluice box; sluice gate; sluicing
溜槽（洗矿槽）6 questions: 3 multiple choice and 3 typed. Score 5 or more to earn 5 points.
The rule to leave a place exactly as you found it: take your trash home and avoid damaging the land.
“Fill in any hole you dig, and leave no trace.”
Word family / collocations: Leave No Trace principles; leave nothing behind; trace (noun)
无痕（不留痕迹）原则Collecting with permission, following the rules, taking only a few specimens and recording where they came from so that sites last for others.
“Responsible collecting means asking permission and taking only what you can study and care for.”
Word family / collocations: responsible collector; collect responsibly; code of ethics
负责任的采集Something that could cause harm or injury.
“Loose rock above you is a serious hazard.”
Word family / collocations: safety hazard; hazardous (adjective); natural hazard
危险（隐患）Not firmly fixed; likely to slide, fall or collapse.
“Never climb on unstable slopes or old mine walls.”
Word family / collocations: unstable ground; unstable slope; instability (noun)
不稳定的Very fine quartz dust made when rock is cut or ground. Breathing a lot of it over time can seriously damage the lungs.
“Wet the rock before cutting it to reduce silica dust.”
Word family / collocations: respirable silica; silicosis; dust mask
硅尘（石英粉尘）A mask that filters the air you breathe.
“Wear a respirator when you cut rock.”
Word family / collocations: dust respirator; N95; respiratory (adjective)
呼吸防护面罩A place, such as a national park or nature reserve, where the law limits collecting, digging and building.
“Collecting crystals in a protected area can be against the law.”
Word family / collocations: protected site; nature reserve; national park
保护区Protecting natural places and things from damage or loss.
“Conservation keeps rare crystal caves safe for scientists.”
Word family / collocations: nature conservation; conserve (verb); conservationist
保护（保育）To enter someone's private land without permission.
“Entering a closed quarry to look for crystals is trespass.”
Word family / collocations: no trespassing; trespasser; trespass on private land
擅自闯入Buying stones from sellers who can show they were mined legally, safely and fairly, with workers paid properly and the environment protected.
“Ask for proof of ethical sourcing before you buy a gem.”
Word family / collocations: ethically sourced; source (verb); fair trade
道德采购（合乎道德的来源）6 questions: 3 multiple choice and 3 typed. Score 5 or more to earn 5 points.
The crystal system with three axes of equal length, all at right angles. Halite, pyrite, fluorite and diamond are cubic.
“Fluorite crystals are cubic, so all three axes have the same length.”
Word family / collocations: cubic system; isometric; cube (noun)
立方（等轴）晶系的The crystal system with three axes at right angles; two are equal and the third is a different length, like a square-ended box.
“Zircon crystals are tetragonal.”
Word family / collocations: tetragonal system; tetragonal prism; tetra- (four)
四方晶系的The crystal system with three axes at right angles, all of different lengths.
“Topaz crystals are orthorhombic.”
Word family / collocations: orthorhombic system; rhombus; ortho- (straight)
正交（斜方）晶系的The crystal system with three equal axes in a flat plane at 120 degrees to each other, plus a fourth axis at right angles to them.
“Beryl, the mineral of emerald, is hexagonal.”
Word family / collocations: hexagonal prism; six-sided; hexagon (noun)
六方晶系的The crystal system with three-fold symmetry: turn the crystal 120 degrees around its main axis and it looks the same. Quartz, calcite and corundum are trigonal.
“Quartz is trigonal, so its lattice repeats every 120 degrees around the long axis.”
Word family / collocations: trigonal system; rhombohedral; three-fold
三方晶系的The crystal system with three unequal axes. Two meet at a right angle and the third is tilted.
“Gypsum crystals are monoclinic, so one axis leans.”
Word family / collocations: monoclinic system; mono- (one); -clinic (leaning)
单斜晶系的The crystal system with three unequal axes, none at a right angle. It has the least symmetry of all seven systems.
“Turquoise and kyanite are triclinic.”
Word family / collocations: triclinic system; tri- (three); -clinic (leaning)
三斜晶系的A shape with two matching ends and long, flat, parallel sides, like a pencil. Many crystals grow as prisms.
“A quartz crystal is a six-sided prism with a pointed tip.”
Word family / collocations: prismatic habit; hexagonal prism; prism (glass that splits light)
棱柱The pointed or flat end of a crystal, where growth stopped.
“A Herkimer diamond has a termination at both ends.”
Word family / collocations: doubly terminated; terminated crystal; terminate (verb)
晶体顶端（晶尖）An imaginary line through a crystal, used to describe its shape and symmetry. The plural is axes (AK-seez).
“If you turn the crystal 120 degrees around this axis, it looks the same.”
Word family / collocations: crystal axes; axis of symmetry; x-axis, y-axis, z-axis
轴（晶轴）6 questions: 3 multiple choice and 3 typed. Score 5 or more to earn 5 points.
Ten famous crystal places. Tap a numbered dot to jump to its card. Two of them are in Hunan province, China.
Simple equirectangular map drawn from Natural Earth land data (public domain). The two Hunan mines are only about 80 km apart, so their dots are shown slightly apart with thin lines to the true spots. Minas Gerais is a state-level point. On a narrow screen, slide the map sideways.
For each spot you will find what forms there, why it forms there, whether you can really collect there, safety and legal notes, a story, and a difficulty rating. “Hunter difficulty” means how hard it is for a normal person to get a specimen from the ground there (1 = easy family dig, 5 = not possible). Facts were checked against the sources listed at the end. Rules, prices and opening times change, so always check before you travel.
Never enter abandoned mines, never trespass, never collect in a protected area without a permit, and always go with an adult. Many of these places are closed on purpose.
Giant, clear-to-milky beams of selenite, the crystal form of gypsum. The biggest are about 11–12 metres long and weigh many tonnes.
A pool of hot, mineral-rich water sat in a cavity about 300 metres underground, heated by a magma body below. The water stayed near 58 °C, a temperature where gypsum slowly crystallizes. Because the water cooled so little, only a few seeds formed, and each one fed for at least 500,000 years.
Closed to everyone except scientists. Flooded again since 2015. You cannot collect here. Miners found the cave in 2000 while digging a new tunnel in a lead-zinc-silver mine. Inside, the air is about 58 °C and almost 100% humid, so even scientists wore cooling suits and breathing masks and could stay only a short time. Pumps kept the mine dry until 2015, then the cave began to flood again.
Legally and physically off limits. Lesson for hunters: if a place can kill you in minutes, it is not a place for a hobbyist.
Gypsum has a Mohs hardness of only 2, so you can scratch it with a fingernail. These crystals are among the softest giants on Earth. They are huge not because they are strong, but because the cave was calm and stable for so long.
地下约300米的巨型石膏（透石膏）晶体，最长约11—12米；洞内约58℃、湿度近100%，现已不对公众开放。
Very clear, naturally faceted quartz crystals with a termination at both ends and about 18 faces. They are not diamonds. Their hardness is 7.
The crystals grew in small cavities (vugs) inside a Cambrian dolostone, a sedimentary rock about 500 million years old. Silica-rich water seeped into the cavities, and quartz grew freely into open space, so both ends of the crystal could develop a point.
Public fee digs. You keep what you find. Several private mines near Middleville, NY, let the public dig for a daily fee. Bring a hammer, a chisel, safety glasses, gloves and sturdy shoes. Many families also search the mine's tailings. Check each mine's current opening season and prices before you go.
Easy and legal on private land, with the owner's rules. Always wear eye protection. Flying chips can injure eyes.
The name is a trick: they are quartz, not diamond. Because they are so sparkly and so perfectly shaped, people once thought someone had cut them. Some contain tiny black specks of carbon-rich material or small water bubbles.
纽约州的“赫基默钻石”其实是两端都有晶尖的透明石英，产于约5亿年前的白云岩空洞中；私人矿场付费可挖，所得归己。
Clear quartz points and clusters. Some crystals are bigger than your hand.
The Ouachita Mountains were squeezed and folded about 300 million years ago. Hot, silica-rich water then flowed through cracks in the folded sedimentary rocks. As it cooled, quartz crystallized on the walls of those cracks and cavities.
Fee digs plus a free surface-collecting area in the national forest. Mount Ida calls itself the “Quartz Crystal Capital of the World.” Fee-dig mines around town let visitors dig for a daily price. The U.S. Forest Service also allows free surface collecting for personal use at Crystal Vista in the Ouachita National Forest (no commercial sale). Rules and prices change, so check before you go.
Easy. Follow the posted rules, stay on public land or paid mine areas, never dig on private land without permission, and bring water in summer.
In World War II, military radios needed quartz crystals that vibrate at an exact frequency. The U.S. government bought Arkansas quartz for that purpose. The Ouachitas are also unusual because the ridges run east–west instead of north–south.
阿肯色州欧乔奇塔山区的热液石英，约3亿年前造山运动后形成；付费矿场可挖，国家森林区可免费地表采集（仅限个人）。
Tourmaline in many colors, aquamarine, morganite, topaz and big quartz crystals. Near Ouro Preto, the rare orange-pink “imperial topaz.”
Around Araçuaí and Governador Valadares, huge pegmatites cooled slowly from water-rich magma, leaving room for giant gem crystals. Imperial topaz near Ouro Preto is different: it grew from hot water (hydrothermal) in veins, not in a pegmatite. Brazil’s ancient rocks hold a lot of lithium, boron and beryllium, the ingredients for tourmaline and beryl.
Licensed mines and dealers. Visit museums, buy with provenance. Almost all land is under mining licences, often small family or cooperative mines (garimpos). Tourists can visit gem shops and mineral museums, including in the historic city of Ouro Preto. If you buy a stone, ask the seller for its locality and provenance.
Not a place for random digging. Mines can be unstable and are private. Go with a licensed guide or visit a museum.
The state’s name means “General Mines.” The gold rush that began in the 1690s gave the region its name. Later, miners found that the ‘ugly’ rock around the gold sometimes hid some of the world’s best gems.
巴西米纳斯吉拉斯州盛产电气石、托帕石、海蓝宝等；伟晶岩缓慢冷却可长出大晶体；多为持证矿山，可参观博物馆和正规店铺。
Deep-blue azurite, green malachite, colorless to white smithsonite, emerald-green dioptase, and more than 300 mineral species in total (counts vary by source).
A pipe-shaped ore body in dolomite rock carried copper, lead, zinc and many other metals. Over millions of years, oxygen-rich groundwater slowly changed the top part of the ore body (the oxidation zone), turning plain sulfides into colorful carbonates and other minerals.
Mining has ended; the old mine is closed to collectors. See specimens in museums. The mine is closed and the old workings are dangerous. Today the best way to see Tsumeb minerals is in major museums and in the care of specialist dealers. Ask for provenance.
Do not enter old mines. Collapse, bad air and flooding kill people every year.
Tsumeb is the type locality of dozens of minerals, meaning they were first scientifically described there. Mineral collectors rank it among the richest mineral localities ever found.
楚梅布矿含300多种矿物（说法不一），以蓝铜矿、孔雀石等闻名；矿山已关闭，可在博物馆观赏。
Clear rock crystal and gray-brown smoky quartz, often in beautiful clusters lining open cracks called fissures or “clefts.”
As the Alps rose, the granite cracked. Groundwater heated by the hot rock dissolved quartz, flowed through these cracks and re-deposited quartz as crystals on the walls. The cracks stayed open inside the mountain, so the crystals could grow with room to spare.
Visit only on a guided power-plant tour. Collecting needs a permit in the protected area. The Gerstenegg cleft, found in 1974 and protected the same year, can be seen only on the guided “Grimsel Undergrund” tour of the power plant (check the dates; it is seasonal). Collecting elsewhere in the Grimsel area is controlled by the canton of Bern. You need a permit, and there are rules about where and how.
Alpine hunting is real mountaineering. Strahler (crystal hunters) train for years. Beginners should go with a guide.
Switzerland has a centuries-old tradition of crystal hunters called Strahler. Gerstenegg was found on 4 October 1974 while engineers were building power-plant tunnels, and the Bern government protected it within months.
阿尔卑斯造山运动中，花岗岩裂隙里热水沉淀出水晶和烟晶；格里姆瑟尔水晶洞只能随导览参观，采集需许可证。
Red rubies, blue sapphires and red spinel, plus other gems. The best rubies are deep red, sometimes called “pigeon’s blood.”
Limestone was heated and squeezed (metamorphism) into marble when India collided with Asia. Hot fluids inside the marble allowed aluminum oxide to crystallize as corundum. Chromium impurities turned it red. Weathering then washed rubies into river gravels (alluvial deposits).
Restricted and unsafe. Check government travel advice. Not for tourists. Locals dig and wash gravel using hand tools and pumps. Foreign visitors have faced restrictions, and parts of Myanmar are affected by conflict. Please do not plan a trip here. The safest way to learn is through museums, books and ethical sourcing.
Unsafe. Treat this entry as ‘read and learn’ only. Buying gems with unclear origin can fund harm. Ask about ethical sourcing.
Mogok is also called the “Valley of Rubies.” Rubies and spinel are so similar in color that famous “rubies” in royal crowns were later found to be spinels. The red in both comes from chromium.
缅甸抹谷以红宝石、尖晶石闻名；大理岩中的刚玉含铬而呈红色。该地区受限且不安全，仅作了解，请勿前往。
Translucent green fluorite cubes and multi-faced crystals with a glassy luster. Its Mohs hardness is 4, and fluorite is the mineral that gave the word fluorescence its name.
Hot, fluorine-rich fluids, linked to granite magma, moved through cracks in older rocks. As they cooled and reacted with calcium-rich rocks, fluorite crystallized in open spaces. Hunan sits in southern China’s great belt of granite-related tin, tungsten and fluorine deposits.
Commercial mine. Not open to collectors. Learn from museums. This is a working mine on controlled land. Mining without a licence is illegal in China. For a 12-year-old in Beijing, the best trip is the Geological Museum of China in the Xisi area, which has minerals from across China (check opening hours and booking first).
Closed to collectors. Do not trespass. Explore through museums, collections and licensed dealers.
Fluorite in a cube is a perfect picture of a cubic lattice. It also cleaves into octahedra, so you can break a cube and get a diamond-shaped solid.
湖南郴州临武香花铺产绿色萤石（硬度4，立方晶系）；矿山不对采集者开放，可去北京的中国地质博物馆学习。
Wolframite (a dark, heavy tungsten ore) together with fluorite in purple, green and blue, quartz and calcite.
In the Late Jurassic (about 150 million years ago), granite magma pushed hot, metal-rich water into cracks in older rocks. The water cooled in quartz veins, depositing tungsten ore and, in open pockets, glittering fluorite and calcite crystals.
Commercial tungsten mine. Not open to collectors. See museum and dealer specimens. Yaogangxian is a tungsten mine, so the most valuable thing is the ore, not the crystals. Mineral specimens reach the world through the mine’s official channels and dealers. Ask for provenance before you buy.
Closed. Underground mines can have collapse, bad air and flooding. Never enter one.
Tungsten has the highest melting point of any metal, 3,422 °C, which is why it was used in old light-bulb filaments. A fluorite-wolframite mine is a picture of hot water and stone working together.
湖南宜章瑶岗仙是钨矿山，伴生萤石、石英、方解石；矿山不对公众开放，可通过博物馆了解。
Diamonds, including some very large ones. The mine is also known for rare blue diamonds, and it produced some of the world’s largest gem-quality diamonds.
Diamonds form deep in Earth’s mantle, at least 150 kilometres down, where pressure and heat are enormous. Rare, fast, gas-rich volcanic eruptions rushed up in carrot-shaped pipes of kimberlite. They carried diamonds to the surface before they could change into graphite.
Working mine. Surface tours only; you cannot collect. Cullinan is an active mine run by a company, and visitors can take a surface tour in the town of Cullinan. Diamonds are not for amateur collecting here. Gem diamonds are heavily regulated, and conflict-free sourcing is important worldwide.
Industrial mine. Tour only. Never enter the fence or the pit.
On 26 January 1905, the mine’s surface manager saw a huge crystal gleaming in the pit wall. The 3,106-carat (about 621 g) stone was the largest gem-quality rough diamond ever found. It was cut into nine major stones, and the two largest are now in the British Crown Jewels.
南非库里南金刚石矿：金伯利岩管把深部地幔的钻石带到地表；1905年发现3106克拉原石；仅可参加地表参观，不可采集。
A crystal is a solid whose atoms or ions sit in a repeating three-dimensional pattern called a lattice. The smallest repeating block is the unit cell.
The dark dots are ions in the lattice; the pale blue dots are ions still dissolved.
Slow cooling means few seeds and lots of time: big crystals. Fast cooling means many seeds that compete: tiny crystals. Very fast cooling (like lava hitting water) can freeze the atoms in a disorderly pattern and make volcanic glass, which is amorphous. Drag the slider.
Naica’s water stayed near 58 °C for at least 500,000 years. If an 11 m crystal grew for 500,000 years, its average growth is only about 0.022 mm per year, which is thinner than a human hair. That is what “slow” means. (See the maths problems below.)
Big crystals need room, time and a steady supply. Pegmatites, hydrothermal veins, cavities (vugs, geodes) and cracks (fissures) provide that.
Every crystal fits one of seven systems, defined by the lengths of its axes (a, b, c) and the angles between them. Combine the systems with all the possible patterns of atoms and you get exactly 14 Bravais lattices and 230 space groups. Some books count trigonal inside the hexagonal family, which gives six families.
The sketches are simplified unit-cell shapes. For the hexagonal system the drawing shows the typical six-sided prism. For trigonal, the rhombohedron is drawn with three equal edges and equal, non-right angles.
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The interactive exercise needs JavaScript.
Friedrich Mohs ranked ten minerals in 1812 by which one scratches which. The numbers show order only. Diamond (10) is not twice as hard as feldspar (6): measured by a scratching machine, diamond is about 20 times harder than feldspar. The chart shows approximate absolute hardness.
Approximate absolute hardness on a sclerometer scale (Wikipedia, “Mohs scale of mineral hardness”).
| Tool | Mohs hardness |
|---|---|
| Fingernail | about 2.5 |
| Copper coin | about 3.5 |
| Iron nail | about 4.5 |
| Glass plate or steel knife | about 5.5 |
| Steel file | about 6.5 |
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| Mineral | Density (g/cm³) |
|---|---|
| Gypsum | 2.3 |
| Quartz | 2.65 |
| Calcite | 2.71 |
| Fluorite | 3.18 |
| Pyrite | about 5.0 |
| Material | Refractive index n |
|---|---|
| Air | 1.00 |
| Water | 1.33 |
| Quartz | about 1.54 |
| Diamond | about 2.42 |
Density = mass ÷ volume. Snell’s law: n₁ sin θ₁ = n₂ sin θ₂. Critical angle: sin θc = n₂ ÷ n₁ (inside a diamond, n₂ = 1 for air). Euler: V − E + F = 2.
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The interactive exercise needs JavaScript.
Crystals can grow in your kitchen. The best choice is alum (in China: 明矾, míngfán, potassium aluminium sulfate, often sold in pharmacies or supermarkets). It makes clear, eight-sided (octahedral) crystals. Easier choices: table salt (cubes, but they are small) or sugar (rock candy, about a week).
For salt or sugar: dissolve as much as you can in hot water, pour the clear liquid into a jar, hang a string or a skewer in it, and leave it for days. Rinse the string in the solution first so that crystals have a rough surface to start on.
| Day | Length (mm) | What I see |
|---|---|---|
| 0 | ||
| 1 | ||
| 2 | ||
| 3 | ||
| 5 | ||
| 7 |
Think and write (3 sentences): (1) What was your prediction for the crystal’s shape, and was it right? (2) Why did cooling make crystals appear? Use supersaturation and nucleation. (3) What happened to the growth rate over time? Calculate your average growth in mm per day.
Every task gives feedback straight away. Try each one before you look at the model answer.
Imagine opening a door and stepping into a room as hot as a sauna, where the air is so wet that sweat cannot evaporate from your skin. Around you, pale beams as long as school buses lean across the floor like fallen tree trunks. This is the Cave of the Crystals in Naica, Mexico, and almost nobody has ever stood inside it.
In the year 2000, two miners were digging a new tunnel about 300 metres underground when they broke into a hidden cavity. The mine was already famous for lead, zinc and silver, but the cave was something else. Its crystals were made of selenite, the clear form of gypsum, a mineral so soft that a fingernail can scratch it. Some of the crystals were more than eleven metres long.
Scientists soon worked out why the crystals were so large. For hundreds of thousands of years, hot water had filled the cave. A body of magma deep below kept the water close to 58 degrees Celsius. At that temperature the mineral anhydrite slowly dissolves while gypsum slowly grows, and the temperature barely changed. Because the water cooled by only a tiny amount, the solution was just barely supersaturated, so only a few seeds formed, and each seed was fed for a very long time. Researchers estimate that the biggest crystals grew for at least 500,000 years, adding a layer thinner than a human hair every year.
The same conditions that built the crystals made the cave dangerous. Without protection, a person can survive only about ten minutes before the heat becomes life-threatening. Explorers wore cooling suits and breathing masks, and even so their work shifts were short. All the while, the mine's pumps ran day and night to keep groundwater out of the tunnels. In 2015 the pumping stopped, and the water began to rise again.
The Naica story teaches an important lesson: the largest crystals do not need violence or speed. They need stability and patience. It also raises a difficult question. When a place is this rare, who should be allowed to enter? Compare it with a family dig in New York, where visitors split open rock for a few hours and go home with a crystal. Both places hold crystals, yet the rules, risks and rewards are completely different. Perhaps, in the end, the returning water is doing what no law could: keeping the cave safe, and giving the crystals a chance to grow once more.
About 410 words. Original text written for this class. Facts from the Naica sources listed at the end.
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A strong scientific paragraph has three parts.
| Test | Mystery crystal | Quartz | Calcite |
|---|---|---|---|
| Hardness | scratches window glass and a steel file | 7 | 3 |
| Weak acid | no fizzing | no fizz | fizzes |
| Breaks | curved fracture, no flat planes | conchoidal fracture | 3 cleavage directions |
| Specific gravity | 2.65 | 2.65 | 2.71 |
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Paraphrase = same meaning, new words and new structure, same length. Summary = only the main idea, much shorter. Steps: (1) read twice; (2) cover the text; (3) write from memory; (4) check that facts and technical terms are right; (5) cite the source if you copy a phrase.
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A collocation is a pair of words that go together naturally. Learn verbs with their nouns: not “do a permit” but “apply for a permit”.
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You already know a lot about crystals, so now you are the teacher. Choose one crystal from your own collection (or one of the ten spots). First write your script of 150 to 200 words. Then film a 2 to 3 minute teaching video and use at least 8 words from the 100-word list.
Film tips: good light, hold the crystal close, speak slowly, and do two or three takes. Practise with the timer first. Speak English only; you can use your script as notes, but try not to read every word.
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Prepare both sides. A good debater can argue against their own opinion first.
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The interactive exercise needs JavaScript.
The interactive exercise needs JavaScript.
The interactive exercise needs JavaScript.
Write first. The model answer appears only after you reach the minimum number of words. Use at least five words from the list. Your draft is saved on this device.
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This quiz remembers which words you know and brings back the hard ones sooner. Words you answer correctly move to a higher box and come back after 1, 3, 7, 14 and then 30 days. Do a short session every day.
Progress is saved only in this browser.
Send Reed your teaching video in WeChat (2 to 3 minutes).
Only send it to your teacher in WeChat. Do not say your full name, school, or address in the video. Showing just your hands and your crystals is fine. Mistakes are fine too; I will watch it and reply with feedback and your next class.
WeChat ID: EnglishTeacherReed
Open WeChat, find Teacher Reed (scan the QR code or search the ID), paste the message, and attach your video. A video on your phone is best. If the file is too big, ask a parent to help or tell me.
All photographs were found on Wikimedia Commons under open licenses (CC0, CC BY, CC BY-SA or public domain). They were resized and compressed for this page and stored on this site. No photographs of people are used except the tiny figure for scale in the Naica photo. Map land shapes: Natural Earth, public domain. Diagrams and text are original.
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