Orthoclase
| Orthoclase | |
|---|---|
 | |
| General | |
| Category | Silicate meeneral |
| Formula (repeatin unit) | KAlSi3O8 |
| Creestal seestem | Monoclinic (2/m) space group C2/m |
| Identification | |
| Colour | Colourless, Greenish, Greyish yellae, White, Pink |
| Creestal habit | Can be anhedral or euhedral. Grains are commonly elongate wi a tabular appearance. |
| Twinnin | Typically displays carlsbad twinnin. Baveno an manebach twins hae an aa been reportit in orthoclase. |
| Cleavage | Haes perfect cleavage on {001} an guid cleavage on {010}. Cleavages intersect at 90°. It can be difficult tae see cleavage in thin section due tae orthoclase's law relief. |
| Mohs scale haurdness | 6 (definin mineral) |
| Skinkle | Vitreous, pearly on cleavage surfaces |
| Streak | white |
| Diaphaneity | Transparent tae translucent |
| Speceefic gravity | 2.55–2.63 |
| Optical properties | Biaxial (-), 2V = 65–75 |
| Refractive index | nα = 1.518–1.520 nβ = 1.522–1.524 nγ = 1.522–1.525 |
| Birefringence | 0.0050–0.0060 |
| Dispersion | relatively strang |
| Extinction | parallel tae cleavage |
| Diagnostic featurs | Distinguishable frae microcline bi a lack in gridiron twinnin. Distinguishable frae sanidine bi a lairger 2Vx. |
| Ither chairacteristics | Law negative relief |
| References | [1][2][3] |
Orthoclase (endmember formula KAlSi3O8) is an important tectosilicate mineral which furms igneous rock. The name is frae the Greek for "straight fracture," acause its twa cleavage planes are at richt angles tae ilk ither. Alternate names are alkali feldspar, potassium feldspar an K-feldspar. The gem kent as muinstane is lairgely componed o orthoclase.