quartz - teaching student specimens of milky quartz, very slightly gray from natural radiation - Unit of 10 smaller 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.
Purple quartz (amethyst) is caused by ferric iron. Small amounts of titanium, iron or manganese cause the pink coloration of rose quartz, and iron may also be the cause of the color of the yellow quartz, citrine, though this is under debate. Natural citrine is very rare. When amethyst is heated, it becomes yellow. Almost entirely, the clusters of citrine crystals being sold are heat treated amethyst.
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.
This milky quartz was collected at the Gold Nugget Mine in Yuma County, Arizona. These are smaller than our normal student specimens, but are large enough and economical, as well.
Want to know more? The Quartz Page is the work of German mineral collector Amir Chossrow Akhavan. When you go there, read "About this Site" before you do anything else. I highly recommend it.
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