Optical properties - Anorthoclase
Crystal System: Triclinic
Color in PPL
PPL may refer to:* people* phospholipid * Pakistan Premier League, Pakistani soccer league* Pay per lead, method of marketing* Pontypool and New Inn railway station, Wales; National Rail station code PPL...

Pleochroism is an optical phenomenon in which a substance appears to be different colors when observed at different angles with polarized light.- Background :Anisotropic crystals will have optical properties that vary with the direction of light...

Cleavage/Fracture Habit: Has perfect cleavage parallel to {001} and good cleavage on {010}.
Crystal twinning
Crystal twinning occurs when two separate crystals share some of the same crystal lattice points in a symmetrical manner. The result is an intergrowth of two separate crystals in a variety of specific configurations. A twin boundary or composition surface separates the two crystals....

Birefringence, or double refraction, is the decomposition of a ray of light into two rays when it passes through certain anisotropic materials, such as crystals of calcite or boron nitride. The effect was first described by the Danish scientist Rasmus Bartholin in 1669, who saw it in calcite...

Typically first-order white (0.0070-0.0080)
Extinction Habit/Angle:
Length Slow/Fast:
Optic Sign: Biaxial negative
2Vx: Calculated 64-74°; Measured 34-60°
Alteration: Commonly weathers to clay minerals
Clay minerals
Clay minerals are hydrous aluminium phyllosilicates, sometimes with variable amounts of iron, magnesium, alkali metals, alkaline earths, and other cations. Clays have structures similar to the micas and therefore form flat hexagonal sheets. Clay minerals are common weathering products and low...

Distinguishing Characteristics:

The mineral anorthoclase ((Na,K)AlSi3O8) is a crystalline solid solution
Solid solution
A solid solution is a solid-state solution of one or more solutes in a solvent. Such a mixture is considered a solution rather than a compound when the crystal structure of the solvent remains unchanged by addition of the solutes, and when the mixture remains in a single homogeneous phase...

 in the alkali feldspar
Alkali feldspar
The alkali feldspar group are those feldspar minerals rich in the alkali elements like potassium. The alkali feldspars include: anorthoclase, microcline, orthoclase and sanidine....

series, in which the sodium-aluminium silicate member exists in larger proportion. It typically consists of between 10 and 36 percent of KAlSi3O8 and between 64 and 90 percent of NaAlSi3O8.
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