Orthoclase, or orthoclase feldspar (end-member formula KAlSi3O8), is an important tectosilicate mineral that forms igneous rock. Its name comes 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, and it is a common constituent of most granites and other felsic igneous rocks, often forming huge crystals and masses in pegmatite. The gem known as moonstone is largely composed of orthoclase. In this atlas it is the mineral species that moonstone records, kept apart from the broader feldspar entity.
Facts
Chemical Formula Hardness (Mohs)The Wikipedia article names orthoclase as the defining mineral for 6 on the Mohs scale. Classification
Crystal System Classification Connections
Classified As
Entity-backed identity for the material classification this material already carries as an enum fact, pointing at the class subcategory of the same name. The enum fact itself stays on the entity unchanged.
Crystallizes In System
Entity-backed identity for the crystal system this mineral already carries as an enum fact, phase 3 bucket conversion (docs\design_entity_backed_browse_buckets_20260928.md, w-bucketconv-divmore2-0929). The original fact stays on the entry unchanged.
In Discipline
In the Other Atlases
- Also in Divinity Atlas: Moon Stone, mineral species of there.
Sources
1. Orthoclase (Wikipedia)
Wikimedia FoundationOrthoclase, lead paragraph
is an important tectosilicate mineral which forms igneous rock
Orthoclase, article text
The gem known as moonstone (see below) is largely composed of orthoclase.
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