Quartz

COLOR

Grey. Takes a good polish.

REFLECTANCE

Quite Low. The mineral is almost black in oil.

ANISOTROPISM

Masked by extensive, light internal reflections.

TEXTURE

Quartz shows a strong tendency to develop idiomorphically. Because its is generally formed very early, it is often replaced by ore minerals or carbonates. It is sometimes zoned.

ASSOCIATED MINERALS

All the minerals.

CRITERIA OF DETERMINATION

This mineral is so common, that it may be expected to be found everywhere. The very low reflectance, complete absence of cleavage, hardness (which may be verified with a needle) and common euhedral habit, are the main criteria.

Source

ATLAS OF ORE MINERALS (P. Picot and Z. Johan)