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Hard facts.

Crystal and Mineral, Field Guide, A to Z

Formula and MohsReal localitiesLore labeled

This field guide covers the types of crystals in the shop, A to Z, with the science first and the lore labeled as lore. Each guide gives the formula, the hardness, the real places the mineral is mined, how to spot a fake and how to care for it.

A to Z.

Crystals and minerals A to Z

Crystals and minerals A to Z, each with its chemistry, hardness, localities and care.

AgateBanded chalcedony that fills holes in rock one thin layer at a time, in every earth color.Mohs 6.5 to 7AmazoniteBlue-green feldspar colored by traces of lead, famous from the Pikes Peak granite of Colorado.Mohs 6 to 6.5AmberTree resin hardened into a fossil over millions of years, light enough to float in salt water.Mohs 2 to 2.5AmethystPurple quartz colored by traces of iron and natural radiation, and the February birthstone.Mohs 7AmmoniteThe fossil shell of an extinct sea animal related to squid, gone for 66 million years.Mohs 3 to 4ApophylliteClear to green square crystals that grow with zeolites in the old lava flows of western India.Mohs 4.5 to 5Aura QuartzNatural quartz coated with a thin film of metal in a vacuum chamber; the rainbow is man-made.Mohs 7 coreAventurineQuartz rock that sparkles with flat flakes of green mica, hematite or other minerals.Mohs 6.5 to 7CelestitePale blue strontium sulfate, soft and heavy, best known from Madagascar geodes; sunlight fades it.Mohs 3 to 3.5CitrineYellow to orange quartz; natural citrine is uncommon, and most on the market is heated amethyst.Mohs 7Clear QuartzColorless quartz, or rock crystal: silicon dioxide with almost nothing else inside.Mohs 7Desert RoseGypsum or barite blades that grew in desert sand, trapped the sand and came out shaped like a rose.Mohs 2Fire AgateBrown chalcedony with iron oxide layers thin enough to flash rainbow colors as the stone turns.Mohs 6.5 to 7FluoriteCalcium fluoride in nearly every color, Mohs 4, and the mineral that gave fluorescence its name.Mohs 4Gem SilicaTranslucent blue chalcedony colored by copper-bearing chrysocolla, mined from copper deposits.Mohs 6.5 to 7KunzitePink to lilac spodumene, colored by manganese, that slowly fades in strong light.Mohs 6.5 to 7KyaniteBlue bladed aluminum silicate that is soft along its length and hard across it.Mohs 4.5 to 7LarimarBlue pectolite mined in one corner of the Dominican Republic and nowhere else on Earth.Mohs 4.5 to 5Lepidocrocite QuartzQuartz with red flakes and threads of lepidocrocite, an iron mineral, sealed inside.Mohs 7LepidoliteLilac lithium mica that glitters, peels into thin flakes and scratches easily.Mohs 2.5 to 3.5Lithium QuartzBrazilian quartz clouded lavender, pink or gray by fine inclusions the trade credits to lithium.Mohs 7Milky QuartzWhite quartz clouded by millions of tiny fluid bubbles, and the most common quartz there is.Mohs 7Pink AmethystPale pink quartz from geodes in Patagonia, Argentina, sold under the amethyst name.Mohs 7Pink OpalSoft pink common opal, mostly from Peru: silica with water locked inside and no flashes of color.Mohs 5.5 to 6.5PyriteIron sulfide: the brassy fool's gold that grows its own cubes and rusts in damp air.Mohs 6 to 6.5Rainbow MoonstoneWhite labradorite feldspar with a blue and rainbow flash, sold under the moonstone name.Mohs 6 to 6.5Rose QuartzPink quartz colored by microscopic mineral fibers, usually massive rock rather than crystals.Mohs 7Ruby in FuchsiteOpaque ruby crystals in green mica, colored red and green by the same element: chromium.Mohs 2 to 9ScoleciteWhite zeolite that grows in sprays of thin needles, named for the way it curls like a worm when heated.Mohs 5 to 5.5Smoky QuartzQuartz turned brown to black by natural radiation in the granite it grew in.Mohs 7Spirit QuartzQuartz, usually amethyst, coated in a second growth of tiny crystals, mainly from South Africa.Mohs 7StilbitePeach to white zeolite that grows in bow-tie sheaves inside old lava flows.Mohs 3.5 to 4Super SevenBrazilian amethyst sold as a blend of seven minerals, though most pieces show only a few.Mohs 7Tangerine QuartzClear quartz with a thin orange skin of iron oxide, mostly from Brazil.Mohs 7

Types of crystals: minerals, varieties and trade names

Types of crystals in this guide are mineral species, varieties of those species or trade names. A mineral species has its own chemistry and crystal structure, like quartz or kyanite. A variety is one mineral in a particular color or habit: amethyst, smoky quartz and citrine are all quartz. A trade name is a seller's label, like aura quartz for quartz coated with metal.

A few entries are not minerals at all. Amber is fossil tree resin, and ammonite is a fossil shell. They are in the guide because collectors keep them next to their crystals.

Crystal types by crystal system

Crystal types can also be sorted by crystal system, the symmetry of the atomic structure inside. There are seven: cubic, tetragonal, orthorhombic, hexagonal, trigonal, monoclinic and triclinic. Fluorite and pyrite are cubic, quartz is trigonal, celestite is orthorhombic and kyanite is triclinic. The system often shows in the shape: fluorite makes cubes, and quartz makes six-sided prisms.

Types of gemstones and kinds of crystals

Types of gemstones and kinds of crystals overlap, but they are different lists. A gemstone is a mineral, or sometimes an organic material like amber, cut and polished for beauty and durability. Many crystals in this guide are gem species in rough form: kunzite is the pink to violet gem variety of spodumene, and amethyst and citrine are the classic quartz gems. Hardness decides what wears well, so quartz at Mohs 7 survives daily wear far better than celestite at 3 to 3.5.

Crystal names and meanings

Crystal names carry meanings older than any shop, and most come from Greek, Latin, places or people. Amethyst comes from the Greek amethystos, "not drunk." Kyanite comes from kyanos, "dark blue," celestite from the Latin caelestis, "heavenly," and pyrite from pyr, "fire," because it throws sparks when struck. Kunzite is named for the gem expert George F. Kunz.

The other kind of crystal meaning, the metaphysical kind, is crystal lore. Each guide includes it, labeled as belief rather than chemistry. Questions about buying, labels and care are in the FAQ.

Crystal and Mineral Field Guide A to Z FAQ

How many types of crystals are there?

Many types of crystals exist: around 6,000 mineral species are recognized, and every crystal falls into one of seven crystal systems.

What is the difference between a crystal and a mineral?

The difference between a crystal and a mineral is that a mineral is a naturally formed solid with a set chemistry and an orderly atomic structure, while a crystal is any solid whose atoms sit in a repeating pattern, natural or not. Nearly every mineral is crystalline, but sugar and lab-grown silicon form crystals without being minerals.

Is amber a crystal?

Amber is not a crystal: it is fossilized tree resin, with no orderly atomic structure.

What is the hardest crystal?

The hardest crystal found in nature is diamond, the 10 at the top of the Mohs scale.

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