calcite - calcite cleavage rhombs from China - Unit of 5 student specimens
Calcite, CaCO3, is an extremely common rock forming mineral. In pegmatites it forms large masses and it makes up some limestones almost entirely. It has a large variety of crystal forms, but these do not include the rhombus-shaped pieces that are sold as “calcite crystals.” The rhombs are produced by cleaving calcite in three directions between rows of atoms.
When calcite is free of impurities and is optically clear, it exhibits double refraction. When it is placed above a line drawn on paper and rotated, the drawn line doubles and becomes single depending on the angle of rotation. Some of these specimens are clear enough to demonstrate this. Excellent examples of cleavage rhombs and are a decent size for your students. The pencil is 5 1/2" long, for scale.
We challenge you to find better student specimens from any supplier. These are clean sharp rhombs of variously-colored calcite from China. Clear specimens give double refraction. The photo is representative of what we ship. Click photo once to select, again to enlarge.
We will send some tiny rhombs with each set so you can demonstrate the calcium carbonate response to a drop of hydrochloric acid - it fizzes and releases carbon dioxide.
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