Quartz

Mineral SiO2

About it

Six-sided prisms capped by points, harder than steel, with no cleavage and a glassy, shell-like break. The commonest mineral at the surface; classic crystals come from Arkansas, Brazil, and the Alps.

Type: Mineral
Group: Silicate (tectosilicate), silica group
Formula: SiO2
Hardness (Mohs): 7
Specific gravity: 2.65–2.66
Streak: white
Lustre: vitreous (glassy)
Crystal system: Trigonal
Colours: colourless, white, purple, yellow, smoky brown, black, pink, green
Transparency: transparent, translucent
Cleavage and fracture: none; conchoidal fracture

Typical values: real specimens vary. For more, see mindat.org.

Its varieties

Agate every colour, in bands
Amethyst purple, violet, lilac, reddish purple
Ametrine purple and yellow in separate zones
Aventurine green, blue, orange, red-brown, cream
Binghamite golden yellow, red, brown
Bloodstone dark green with red spots
Blue lace agate pale blue, white
Botswana agate pink, peach, grey, white, brown
Brazilian agate grey, white, brown, red; often dyed blue, green, pink, or purple
Brecciated jasper red, brown, with cream or grey veins
Bruneau jasper brown, cream, red, with concentric eyes
Carnelian orange, red-orange, reddish brown
Chalcedony white, grey, blue, lavender, yellow, brown
Chrome chalcedony emerald green
Chrysoprase apple green, bright green, yellowish green
Citrine pale yellow, golden yellow, orange, orange-brown
Condor agate red, orange, yellow, purple, white, black
Crazy lace agate white, red, yellow, brown, grey
Dendritic agate white, grey, colourless, with black or brown dendrites
Dryhead agate red, orange, white, tan
Ellensburg blue cornflower blue, sky blue
Enhydro agate grey, white, translucent
Fairburn agate red, yellow, orange, brown, black, white
Fire agate brown with iridescent red, orange, green, gold, and blue
Gem silica bright blue, blue-green
Hawk's eye blue-grey, greenish blue, dark blue
Herkimer diamond colourless, sometimes with black specks
Holley blue agate lavender, violet-blue, pale purple
Iris agate colourless to grey; rainbow colours in light passed through
Jasper red, yellow, brown, green, mixed
Kentucky agate red, yellow, black, white, grey
Laguna agate red, orange, pink, purple, yellow, white
Lake Superior agate red, orange, yellow, white, grey, in bands
Milky quartz white, milky white
Montana agate clear, grey, white, with black dendrites and red-brown stains
Morion black, very dark brown
Moss agate colourless or white with green, brown, or black inclusions
Myrickite white, grey, with red patches
Onyx black and white, black, white, brown
Picture jasper tan, brown, cream, red, blue-grey, in scenic patterns
Pietersite blue-grey, gold, brown, swirled
Plume agate clear or white with red, yellow, black, or gold plumes
Polychrome jasper red, brown, cream, pink, yellow, green, swirled
Poppy jasper red, yellow, orange, brown, with round orbs
Prasiolite pale green, leek green
Red jasper brick red, red-brown
Rock crystal colourless, water-clear
Rose quartz pale pink, rose pink
Rutilated quartz colourless or smoky with golden, red, or silver needles
Sagenitic agate clear or white with black, brown, gold, or red needle sprays
Sard brownish red, dark brown
Sardonyx red-brown and white bands
Scottish agate red, pink, white, grey, blue
Smoky quartz light brown, smoky grey, dark brown, nearly black
Spirit quartz purple, lilac, smoky brown, white, golden
Sweetwater agate grey, clear, with black dendrites
Thunder Bay amethyst purple, often with red tips from hematite
Tiger's eye golden yellow, golden brown, red-brown (heated)
Tourmalinated quartz colourless or milky with black needles
Tree agate white with green dendrites

Also silicate (tectosilicate), silica group

Cristobalite, Opal, Tridymite

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