Open Adit™ - Feldspar Group Datasheet

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Feldspar is an important group of rock-forming minerals which make up perhaps as much as 60% of the Earth's crust. Feldspars crystallize from magma in both intrusive and extrusive rocks; they occur as compact minerals, as veins, and are also present in many types of metamorphic rock. Rock formed entirely of plagioclase feldspar is known as anorthosite. Feldspars are also found in many types of sedimentary rock.

Feldspars are distinguished by structure and chemistry. The potassium or K-feldspars are polymorphs, meaning they have the same chemistry, but different structures and therefore are different minerals. The plagioclase feldspars are a set of minerals that are in a series from a sodium rich end member, albite, to a calcium rich end member, anorthite. The intermediate members of the series are given arbitrary boundries based on their percentage of sodium or calcium.

Feldspars are commonly referred to as plagioclase and orthoclase (K-Spar) because identification to greater precision is difficult with ordinary methods. Once identified, however, some feldspar mineral varieties are found to have distinctive characteristics or originate from a classic locality and on these bases are recognized by mineral collectors as belonging to a specific feldspar mineral.

Chemistry:

XAl_(1-2)Si_(3-2)O₈ - General Formula.

The X can be calcium, potassium and / or sodium.

Class

Silicates

Subclass:

Tectosilicates

Group:

Feldspar

Varieties:

Albite, Anorthite, Labradorite, Microcline, Orthoclase, Plagioclase

Crystal:

Monoclinic & Triclinic

Metaphysical Properties

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