MINERAL OF THE MONTH: July 2007: Labadorite

This month’s mineral of the month is Labradorite, which was first discovered in the Labrador Peninsula in Canada. It is also found in Norway, Finland, and Russia. It is truly a captivating mineral that displays a colorful shiller effect when held and moved during observation. The color display is from layers of intergrowth inside the crystal. These intergrowth layers are caused by compatible chemistries at high temperature becoming incompatible at lower temperature that results in a separating and layering of the crystal components. The color effect is caused when light enters the specimen, only to be refracted back and forth by the deeper layers. The refracted light is slowed as it travels through the layers and mixes with other light rays to change and produce a different wavelength of light. The color effect depends on the thickness and orientation of the layers.

Labradorite is a member of the plagioclase series of minerals, which comprises feldspars. It contains sodium, calcium, aluminum, silicon, and oxygen. The color is gray to smoky black. It has a dull to vitreous luster. The crystals are transparent to translucent. It has a conchoidal fracture pattern, a hardness of between 6 and 6.5, and a specific gravity of between 2.70 and 2.74. The flashes of color (labradorescence) can vary between blue, violet, green and sometimes orange and yellow.


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