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Gallery of Feldspars

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Feldspars are a group of closely related minerals that together make up the majority of the Earth's crust. All of them have a hardness of 6 on the Mohs scale, so any glassy mineral that's softer than quartz and cannot be scratched with a knife is very likely to be a feldspar. Learn more about the feldspar minerals.

Feldspars lie along one of two solid-solution series, the plagioclase feldspars and the alkali or potassium feldspars. All of them are based on the silica group, consisting of silicon atoms surrounded by four oxygens. In the feldspars the silica groups form rigid three-dimensional interlocking frameworks.

This gallery starts with plagioclase, then shows alkali feldspar.

Images 1-10 of 10
A gravestone specimenPlagioclase in AnorthositeHand specimens from New YorkPlagioclase Feldspar in AnorthositeEven the back side is gaudyLabradoriteThe dazzling sidePolished Labradorite
Don't take this for granitePotassium Feldspar (Microcline)Two good cleavagesPotassium Feldspar (Orthoclase)On the back of the Willett monumentAlkali Feldspar in Granite PegmatiteRugged good looksPotassium Feldspar (Sanidine)
Typical K-spar colorAlkali Feldspar of Pikes PeakGreen microclineAmazonite (Microcline)
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