Properties
| Category | Tectosilicate minerals |
|---|---|
| Formula | KAlSi3O8 |
| Crystal system | Monoclinic |
| Color | Colorless, greenish, greyish yellow, white, pink |
| Crystal habit | Can be anhedral or euhedral. Grains are commonly elongate with a tabular appearance. |
| Cleavage | Has perfect cleavage on {001} and good cleavage on {010}. Cleavages intersect at 90°. It can be difficult to see cleavage in thin section due to orthoclase's low relief. |
| Fracture | Uneven |
| Mohs scale hardness | 6 (defining mineral) |
| Luster | Vitreous, pearly on cleavage surfaces |
| Streak | White |
| Diaphaneity | Transparent to translucent |
| Specific gravity | 2.55–2.63 |
From the Wikipedia article
Orthoclase, or orthoclase feldspar (endmember formula KAlSi3O8), is an important tectosilicate mineral which forms igneous rock. The name is from the Ancient Greek for "straight fracture", because its two cleavage planes are at right angles to each other. It is a type of alkali feldspar, also known as potassium feldspar or K-spar. The gem known as moonstone (see below) is largely composed of orthoclase.
Source
Source record: crystal-compendium/orthoclase/minerals.json. Fetched from English Wikipedia by the operator 2 October 2026.
https://en.wikipedia.org/wiki/Orthoclase — revision id 1376720321. Text and properties from Wikipedia, licensed CC BY-SA 4.0.