quartz - very slightly gray milky quartz - student specimens UNIT OF 5 SPECIMENS
Quartz is the second most common rock-forming mineral after feldspar. The white color of milky quartz is caused by minute inclusions of fluid, gas or both, which interfere with its optical properties. Natural radiation colors quartz gray. These specimens are only very slightly gray, and are good examples of milky quartz. Useful to show students that milky quartz is variable and for a discussion of the various colors of quartz.
Pure quartz "silica" sand is used in the manufacture of glass. It is melted and cooled rapidly so that the atoms cannot organize into crystals. An unorganized mass of atoms is a characteristic of glass and accounts for its curved conchoidal fracture. Quartz also exhibits this fracture. As an example of this, think of the curved chips in the rim of a carelessly opened bottle.
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