Gemstones
Every gemstone and crystal in the encyclopedia — hardness, composition, colour and origin, plainly explained.
Amethyst
The purple variety of quartz — the most prized member of the quartz family, coloured by iron and irradiation.
GemstoneAquamarine
The sea-blue variety of beryl — emerald's clearer, hardier cousin, coloured by iron.
GemstoneCitrine
The yellow-to-orange variety of quartz — November's warm birthstone, most of it heat-made from amethyst.
GemstoneDiamond
Pure crystalline carbon — the hardest natural material and the enduring symbol of the precious stones.
GemstoneEmerald
The green variety of beryl — valued for its vivid colour despite near-universal inclusions.
GemstoneGarnet
Not one mineral but a whole silicate group — January's birthstone, most familiar in deep red.
GemstoneJade
Two tough minerals sold as one gem — jadeite and nephrite — revered above all in China.
GemstoneMoonstone
A feldspar gem with a floating blue-white glow — adularescence, the "moonlight" sheen.
GemstoneOpal
A hydrated silica gel famous for play-of-colour — soft, water-bearing and unlike any crystalline gem.
GemstonePearl
An organic gem grown by molluscs — soft, lustrous nacre requiring gentle care.
GemstonePeridot
August's vivid green birthstone — gem olivine coloured by its own iron content.
GemstoneRuby
The red variety of corundum — second only to diamond in hardness, and coloured by chromium.
GemstoneSapphire
Corundum in every colour but red — famed for its blue, and prized for durability.
GemstoneTanzanite
A blue-violet zoisite found in just one place on Earth — heat-treated and pleochroic.
GemstoneTopaz
A hard aluminium fluorosilicate spanning colourless to imperial orange — with a notable cleavage to respect.
GemstoneTurquoise
A sky-blue copper phosphate valued for millennia — soft, porous and often stabilised.