Garnet

Quartz
Property	Value	Comments
Formula	SiO₂
Crystal System	hexagonal
Crystal Habit	prismatic hexagonal crystals with horizontally striated faced; sometimes appears dursy: twinning common
Cleavage	seldom distinct
Color/Pleochroism	colorless, white, purple, yellow, brown, pink, blue
Optic Sign	Uniaxial (+)
Refractive Indices omega = epsilon =	1.544 1.553
Max Birefringence	0.009
Distinguishing Features	uniaxial; low relief; low birefringence
Occurrence	Quartz is extremly common and can be found in many types of igneous, sedimentary, and metamorphic rocks.
Editors	Christine Raczka (MHC '08), Caroline Hackett (Smith '14)

	Photomicrograph of quartz under plane polarized light.
	Photomicrographic image of Quartz under cross polarized light. The rollover image shows the wave type of extinction that is common in Quartz.
	Photomicrographic image of quartz under crossed polarized light. The rollover displays the same grain under plain polarized light. Poor cleavage is visible in both images. Note the low relief seen under plain polarized light.
	Undulatory extinction is a common feature of quartz. The rollover image displays the same grain with rotation. Notice, the entire grain never goes completely extinct at once.