Quartz : Type

Major Varieties

Chalcedony	Any cryptocrystalline quartz, although generally only used for white or lightly coloured material. Otherwise more specific names are used.
Agate	Multi-coloured, banded Chalcedony, semi-translucent to translucent
Onyx	Agate where the bands are straight, parallel and consistent in size.
Jasper	Opaque chalcedony, impure
Aventurine	Translucent chalcedony with small inclusions (usually mica) that shimmer.
Tiger's eye	Fibrous gold to red-brown coloured quartz, exhibiting chatoyancy.
Rock crystal or mountain crystal	Clear, colourless
Amethyst	Purple, transparent
Citrine	Yellow to reddish orange to brown, greenish yellow
Prasiolite	Mint green, transparent
Rose quartz	Pink, translucent, may display diasterism
Milk quartz or snow quartz	White, translucent to opaque, may display diasterism
Smoky quartz	Brown to grey, opaque
Morion	Dark-brown, opaque
Carnelian	Reddish orange chalcedony, translucent

Impurity concentrations in natural α-quartz crystals usually fall below 1000 parts per million. The violet and yellow hues observed in amethyst and citrine are associated with Fe, and black smoky quartz contains Al. The white coloration of milky quartz reflects light scattering off minute fluid inclusions, and the pink tint in rose quartz is believed to arise from fine-scale intergrowths of a pegmatitic mineral called dumortierite [Al₂₇B₄Si₁₂O₆₉(OH)₃]. See also Amethyst; Dumortierite.