The crystal encyclopedia

Dark, dense and iron-rich material traditionally kept at doorways and desks.

Sulfide

Acanthite

Silver sulfide, the principal ore of silver, in sooty black crystals with a metallic sheen. Mexican specimens often intergrow with native silver wires.

Mohs 2-2.5 · Black, Lead grey

Pyroxene

Aegirine

Long, sharply striated black-green prisms, most famously from Mount Malosa in Malawi, where they grow with orange zircon and smoky quartz in some of the most photogenic combination specimens of recent decades.

Mohs 6-6.5 · Black, Black-green

Chalcedony

Agate

Banded chalcedony, formed as silica-rich fluid seeped in layers into volcanic cavities. Every agate is a cross-section of its own slow filling, which is why no two slices repeat.

Mohs 6.5-7 · Banded, Grey

Fossil

Agatised Dinosaur Bone

Jurassic sauropod bone in which the marrow cells have been replaced cell by cell with agate and jasper — 'gembone'. The best Utah material shows red and yellow cells outlined in black, holding a mirror polish.

Mohs 6.5-7 · Red, Yellow

Carbonate

Aragonite

Chemically identical to calcite but with a different crystal structure, aragonite grows in radiating sputnik clusters, coral-like sprays and the nacre of shells.

Mohs 3.5-4 · Brown, Orange

Silicate

Axinite

Sharp axe-blade crystals in clove brown with violet flashes, strongly pleochroic and unmistakable once seen.

Mohs 6.5-7 · Clove brown, Violet

Sulfate

Barite

Unusually heavy for a pale mineral — its high barium content makes barite feel like metal in the hand. Grows in blades, roses and elegant tabular crystals.

Mohs 3-3.5 · White, Blue

Fossil

Belemnite

The bullet-shaped internal skeleton of an extinct squid relative. Cut and polished, the calcite shows a radiating fibrous structure from a central apical line.

Mohs 3-4 · Brown, Amber

Tourmaline

Black Tourmaline (Schorl)

Schorl, the iron-rich end of the tourmaline family, grows in deeply striated black prisms with a distinctive rounded-triangular cross-section.

Mohs 7-7.5 · Black

Chalcedony

Bloodstone

Dark green chalcedony flecked with red jasper. Also called heliotrope, it is one of the traditional March birthstones.

Mohs 6.5-7 · Green, Red

Chalcedony

Botswana Agate

Fine grey, pink and lavender banding, often with a tiny druzy quartz eye at the centre. Softer and more muted than Mexican agates, and quietly one of the most beautiful.

Mohs 6.5-7 · Grey, Blush

Pyroxene

Bronzite

Enstatite with enough iron to develop a warm metallic bronze sheen across the cleavage planes. Usually cut as cabochons or beads, sometimes intergrown with green serpentine.

Mohs 5-6 · Bronze, Brown

Carbonate

Cerussite

Lead carbonate with adamantine, almost diamond-like lustre, forming twinned snowflake and reticulated networks. Tsumeb specimens are legendary.

Mohs 3-3.5 · Colorless, White

Silicate

Chiastolite

Andalusite grown with graphite inclusions arranged in a dark cross that appears when the crystal is sliced across. Every cross is slightly different, and the best show four crisp arms with no smearing.

Mohs 6.5-7.5 · Brown, Black

Meteorite

Chondrite Meteorite

The most common meteorite type and the oldest rock anyone can hold: stony material containing chondrules, millimetre droplets of melt that condensed 4.56 billion years ago before the planets existed.

Mohs 5-6 · Grey, Brown

Borate

Colemanite

Glassy colorless borate crystals that grow in blocky, brilliantly lustrous groups. Californian material from the Death Valley borate districts set the standard.

Mohs 4-4.5 · Colorless, White

Fossil

Crinoid

Sea lilies — stalked echinoderms that carpeted Palaeozoic sea beds. Most material is disarticulated stem segments in limestone; complete crowns with the feeding arms intact are dramatically rarer and prepared over many hours.

Mohs 3-4 · Cream, Tan

Oxide

Cuprite

Copper oxide in deep garnet-red cubes and octahedra that glow ruby when back-lit. Namibian Onganja crystals from the 1970s are legendary; the hair-like variety chalcotrichite forms scarlet velvet mats.

Mohs 3.5-4 · Red, Pink-red

Gypsum

Desert Rose

Rosette clusters of gypsum or barite that grow in arid basins, trapping sand grains between their blades so each 'petal' carries the color of the desert it formed in.

Mohs 2 · Sand, Tan

Pyroxene

Diopside

Chrome diopside from Siberia is a deep forest green rivalling emerald; star diopside from India shows a four-rayed black star.

Mohs 5.5-6.5 · Green, Black

Carbonate

Dolomite

A calcium magnesium carbonate that grows in saddle-shaped curved rhombs, often forming the sparkling white matrix beneath more colorful minerals.

Mohs 3.5-4 · White, Pink

Halide

Fluorite

The most colorful mineral in the world, fluorite grows in perfect cubes and octahedra, often color-zoned in bands of green, purple and clear within a single crystal.

Mohs 4 · Green, Purple

Fossil

Fossil Shark Tooth

Sharks shed teeth continuously, which is why they are the most abundant vertebrate fossil on earth. Color comes from the minerals in the burial sediment — river-tumbled Florida teeth run jet black, Moroccan phosphate teeth tan and grey.

Mohs 4.5-5 · Black, Grey

Sulfide

Galena

Lead sulfide that grows in flawless silver-grey cubes with a bright metallic lustre and remarkable weight.

Mohs 2.5-2.75 · Lead grey

Volcanic glass

Gold & Silver Sheen Obsidian

Obsidian with a metallic golden or silver shimmer produced by a layer of aligned microscopic gas bubbles reflecting light in unison.

Mohs 5-5.5 · Black, Golden

Oxide

Hematite

Iron oxide with a metallic mirror surface and a signature red-brown streak. Botryoidal 'kidney ore' from Cumbria and iridescent rainbow hematite from Brazil are the collector forms.

Mohs 5-6.5 · Silver, Black

Pyroxene

Hypersthene

A dark orthopyroxene with a metallic bronze-to-silver sheen from fine exsolution lamellae. Polished Madagascan cabochons show a moving silvery streak against near-black.

Mohs 5-6 · Black, Bronze

Amphibole

Jade (Nephrite)

One of two minerals sold as jade. Nephrite is an interlocking amphibole felt, which makes it the toughest natural stone known — far harder to break than to scratch.

Mohs 6-6.5 · Green, Cream

Chalcedony

Jasper

Opaque microcrystalline quartz colored by iron and clay impurities. Jasper is a family rather than a single stone, and named varieties — ocean, picture, mookaite, bumblebee — often come from a single deposit.

Mohs 6.5-7 · Red, Yellow

Organic

Jet

Fossilised driftwood compressed into a dense, velvet-black coal that takes a mirror polish and weighs almost nothing in the hand. Whitby jet, formed from Jurassic monkey-puzzle wood, is the historical standard and has been carved in Yorkshire for two thousand years. Hard jet is compact and glassy; soft jet cracks with age.

Mohs 2.5-4 · Black

Sedimentary

Kambaba Jasper

Dark green and black orbicular stone built from fossilised cyanobacterial colonies — technically a stromatolite rather than a jasper. The swirling eyes give it an unmistakable reptilian look.

Mohs 6-7 · Bottle green, Black

Feldspar

Labradorite

A plagioclase feldspar that hides fire inside dull grey stone. Light striking internal lamellae scatters into blue, gold, green and, in the best pieces, full-spectrum flash.

Mohs 6-6.5 · Grey, Blue

Chalcedony

Laguna Agate

Widely considered the finest banded agate on earth: tight, high-contrast red and white fortification banding from one ranch in Chihuahua. Collector-grade nodules are sold by name and by pattern.

Mohs 6.5-7 · Red, Orange

Igneous

Larvikite

Norwegian building stone shot with silvery-blue schiller from feldspar exsolution lamellae — labradorescence in a dark grey rock. Widely used as facade cladding, and quietly one of the most beautiful stones in any city.

Mohs 6-6.5 · Grey, Steel grey

Oxide

Magnetite

The most magnetic naturally occurring mineral. Strongly magnetic pieces are called lodestone and will pick up iron filings unaided.

Mohs 5.5-6.5 · Black

Volcanic glass

Mahogany Obsidian

Obsidian streaked with red-brown iron oxide bands, giving a marbled timber-like figure through the black glass.

Mohs 5-5.5 · Mahogany, Black

Carbonate

Malachite

Banded green copper carbonate with concentric bullseye patterning from botryoidal growth. Congolese material sets the standard for contrast and polish.

Mohs 3.5-4 · Green

Sulfide

Marcasite

Chemically identical to pyrite but crystallising in a different system, marcasite is paler, more brittle and prone to breaking down over time.

Mohs 6-6.5 · Pale brass, Silver

Fossil

Megalodon Tooth

The tooth of Otodus megalodon, the largest shark that ever lived, extinct around 3.6 million years ago. Teeth run from palm-sized to over seven inches; every extra half inch above five is a substantial jump in rarity and price.

Mohs 4.5-5 · Black, Grey

Arsenate

Mimetite

Lead arsenate that grows as glassy yellow barrel crystals or as botryoidal 'campylite' spheres. The Mexican Mapimí material, in warm marigold rounds, is the one most often seen.

Mohs 3.5-4 · Yellow, Orange

Chalcedony

Mookaite

Australian radiolarite — silicified deep-sea microfossil ooze — in mustard yellow, plum and brick red. Dense, takes a glassy polish and comes from one station in the Kennedy Ranges.

Mohs 6.5-7 · Red, Yellow

Fossil

Mosasaur Tooth

The conical, ridged tooth of a Cretaceous marine reptile — a lizard that returned to the sea and grew to seventeen metres. Moroccan phosphate beds supply most of the market, often with root and jaw section intact.

Mohs 4.5-5 · Brown, Black

Organic

Mother of Pearl

The nacre lining of pearl oysters and freshwater mussels, cut into plates and cabochons. A soft silvery-white with a slow moving sheen rather than the hard flash of abalone.

Mohs 2.5-4 · White, Cream

Element

Native Silver

Silver in wires, ropes and herringbone crystal groups. Kongsberg produced the finest wire silver ever mined, and specimens from its 340-year run are museum currency.

Mohs 2.5-3 · Silver, Grey

Zeolite

Natrolite

Needle-sharp radiating sprays of sodium zeolite, often clear enough to facet in small stones. It is the matrix mineral that hosts benitoite in California.

Mohs 5-5.5 · White, Colorless

Meteorite

Nickel-Iron Meteorite

Fragments of the shattered cores of early planetesimals: solid iron-nickel that cooled over millions of years, producing the interlocking Widmanstatten pattern revealed by etching.

Mohs 4-5 · Silver, Grey

Metamorphic

Nuummite

One of the oldest gem materials on earth at roughly three billion years — a black amphibole rock threaded with iridescent gold, green and violet flash from intergrown crystal lamellae. Mined by hand from a remote Greenland site with a short seasonal window.

Mohs 5.5-6 · Black, Iridescent

Volcanic glass

Obsidian

Not a mineral at all but volcanic glass, cooled too quickly for crystals to form. Varieties include snowflake, mahogany, sheen, rainbow and the translucent Apache tear.

Mohs 5-5.5 · Black, Mahogany

Chalcedony

Onyx

Chalcedony with straight parallel banding. Most 'black onyx' on the market is grey chalcedony dyed black, a practice so old and so standard that it is not considered a deception.

Mohs 6.5-7 · Black, White

Fossil

Petrified Wood

Ancient wood in which every cell was replaced by silica, preserving growth rings, bark and even insect galleries in solid quartz.

Mohs 6.5-7 · Brown, Red

Sulfide

Pyrite

Iron sulfide that grows in astonishingly perfect cubes, dodecahedra and radiating suns. The Navajun mine in Spain produces cubes so sharp they look machined.

Mohs 6-6.5 · Brass, Gold

Silicate

Rhodonite

Pink manganese silicate laced with black manganese oxide veining. Harder and far more durable than rhodochrosite, which makes it the better carving stone.

Mohs 5.5-6.5 · Pink, Black

Chalcedony

Sardonyx

Straight-banded chalcedony alternating reddish-brown sard with white — the classic cameo material, because a carver can cut through the pale layer to reveal the dark one beneath.

Mohs 6.5-7 · Red, White

Concretion

Septarian Nodule

Mud concretions that dried and cracked internally, then had the cracks filled with golden calcite and brown aragonite — a fossil record of shrinkage roughly fifty million years old.

Mohs 3-4 · Yellow, Brown

Silicate

Serpentine

A group of magnesium silicates named for their scaled, snake-like patterning. Californian serpentine is the state rock and forms the backbone of the Coast Ranges.

Mohs 3-5 · Green, Yellow-green

Carbon

Shungite

A non-crystalline carbon rock, roughly two billion years old, found principally around Lake Onega in Russian Karelia. Elite or noble shungite is over ninety percent carbon and has a bright metallic lustre.

Mohs 3.5-4 · Black

Quartz

Smoky Quartz

Quartz darkened from grey to near-black by natural irradiation of aluminium impurities. Alpine smoky quartz from Swiss and Austrian clefts is among the most sought-after crystal in the world; Scottish cairngorm has been set into ceremonial dress for centuries.

Mohs 7 · Brown, Grey

Sulfide

Sphalerite

Zinc sulfide with a dispersion three times higher than diamond, which makes cut honey-colored Spanish sphalerite one of the most fiery gemstones that exists.

Mohs 3.5-4 · Honey, Red

Silicate

Staurolite

Iron aluminium silicate famous for twinning into natural crosses — some at ninety degrees, some at sixty. Russian Kola material gives the crispest right-angle crosses.

Mohs 7-7.5 · Brown, Clove brown

Sulfide

Stibnite

Long steel-grey blades with a brilliant metallic lustre, growing in dramatic radiating sprays. Chinese specimens from Wuning are among the most spectacular mineral objects ever mined.

Mohs 2 · Steel grey

Cyclosilicate

Sugilite

Deep violet manganese silicate, effectively a single-deposit stone: virtually all gem sugilite comes from the Wessels Mine in the Kalahari manganese field.

Mohs 5.5-6.5 · Violet, Magenta

Quartz

Tiger's Eye

Quartz that replaced fibrous crocidolite, inheriting its parallel structure and producing a rolling band of light called chatoyancy. Blue hawk's eye is the unoxidised form.

Mohs 6.5-7 · Gold, Brown

Quartz

Tourmalinated Quartz

Clear quartz shot through with black schorl tourmaline, producing graphic ink-on-glass patterns. Slabs and spheres show the composition best.

Mohs 7 · Colorless, Black

Phosphate

Turquoise

Hydrated copper aluminium phosphate, prized for six thousand years across Persia, Egypt and the American Southwest. Color ranges from Persian sky blue to Sonoran green, often webbed with matrix.

Mohs 5-6 · Blue, Green

Chalcedony

Turritella Agate

Dark brown agate packed with the spiral shells of freshwater snails — properly Elimia tenera, not Turritella, but the trade name stuck a century ago. Cut faces show the spirals in cross-section like a mosaic.

Mohs 6.5-7 · Brown, Black

Silicate

Zircon

A genuinely brilliant natural gem with dispersion approaching diamond, and quite unrelated to cubic zirconia despite the name confusion. Cambodian material is heat-treated to the familiar electric blue; natural stones run honey, red and brown.

Mohs 6-7.5 · Blue, Golden

Please noteTraditional properties, effects, and aura associations are shared for cultural, historical, and personal-interest reasons only. They are folklore, not medicine. Nothing here is medical, psychological, or financial advice, and no stone is intended to diagnose, treat, cure, or prevent any condition. Please see a qualified professional for health concerns.