Low-birefringence
Equant

Description

Transparent colorless; equant grains; cleavage absent. Grains larger than ~30um show higher order birefringence colors (dark orange, pink), while smaller grains appear white or gray in cross-polarized light. May appear pitted, or show opaque or reddish coatings visible in plane polarized or reflected light. May be well-rounded where aeolian or fluvial transport contributes. Common mineral in detrital sediments and rock fragments.

Imposters

Quartz and feldspar have similar low-order birefringence colors (white to gray) and regularly co-occur. They can be distinguished from each other by cleavage: feldspar has good cleavage, and quartz has no cleavage. That is, if the grain has a straight edge, it is more likely a feldspar, although exceptions occur. Polysynthetic twinning does not occur in quartz, and is a clear indicator of a feldspar when present. However many feldspars do not show such twinning.

External Resources

Quartz on MinDat