How many varieties of quartz do you know? Quartz, a silica and the most common mineral, can occur in many forms. It can be ultra-fine grained (cryptocrystalline) or appears with an extraordinary colour when it contains certain elements or impurities. The charts below are some of the most common varieties of quartz. Some high-pressure forms of quartz such as coesite and stishovite are rare in nature and high-temperature forms such as tridymite and cristobalite can be identified only with a microscope. Varieties of Cryptocrystalline Quartz Note: Chalcedony (pronounced kal-sed-o-nee) is the name for cryptocrystalline quartz. The following are names for varieties of chalcedony known through the centuries. This list is by no means authoritative; no list can be, as there is much confusion, disagreement, and misunderstanding over these varieties and their names. Variety Name Color Causes of Color Chalcedony (Catch-all for colors not described by one of following varieties) Pale gray, blue-gray, blue, black, brown,colorless Impurities Agate Distinctly banded chalcedony with successive layers differing in color or with distinctive patterning Onyx Banded agate with layers of contrasting color in parallel straight lines     Carnelian Translucent blood red to brownish- Red Iron Sard (also called sardius) Translucent light brown to yellowish brown to dark brown Iron Sardonyx Translucent red or brown layers with white layers Moss Agate Gray, bluish or milky transparent to translucent chalcedony enclosing moss-like crystal growths Manganese oxide, chlorite, goethite, hematite, and others Chrysoprase Translucent apple green Colloidal nickel compound Plasma Opaque leek green to dark green Green silicate minerals Prase Translucent leek green Chlorite, pyroxene, or amphibole inclusions Bloodstone (or Heliotrope) Plasma with red spots Hematite or red jasper Jasper Opaque shades,of red,brown, Iron oxides, other compounds Chert Opaque white to light gray   Flint Dark gray to black     Varieties of Crystalline Quartz   Variety Name Colors Causes of Color Rock Crystal Colorless, transparent Iron plus irradiation Amethyst Various shades of purple or violet   Citrine Various shades of yellow, yellow-brown, yellow-orange Iron impurities; mostcitrine is made by heating amethyst Smoky Quartz (also called Cairngorm, or if black, Morion) Pale smoky brown to almost black;can be opaque Aluminum impurities plus irradiation Rose Quartz Pale pink to deep red rose; sometimes shows asterism (star) Titanium Blue Quartz Pale blue, grayish blue to lavenderblue; rare; somewhat chatoyant Scattering of light by tiny needles of rutile or other crystals Green Quartz (Praziolite) Green Iron, heat Milky Quartz Milky white to grayish white;can be nearly opaque Numerous gas and liquid inclusions Quartz Varieties with Inclusions Rutilated Quartz (also catseye, when chatoyant; sagenite, when a netlike pattern) Colorless to yellow,red or brownish acicular (hairlike) crystals included in quartz crystal Contains distinct acicular rutile crystals in sprays or random orientation Tourmalinated Quartz   Black colored acicular (hairlike) fibers inclusions Contains distinct acicular tourmaline crystals Aventurine Green, brick red Green caused by spanglingof minute mica crystals;red,by hematite Tigereye (also hawkseye, with blue chatoyancy from blue asbestos) Fibrous yellow, yellow-brown, brown, reddish brown, bluish, grayish-green, green, chatoyant Formed by replacement of asbestos