silicates
Microcline
K(AlSi3O8)
- Also known as
- amazoniteperthite
- Crystal system
- triclinic
- Hardness
- 6–6.5 on the Mohs scale
- Lustre
- vitreous
- Colour
- White, cream, salmon, and green as amazonite
- Where it forms
- In granites and especially in pegmatites, where it can form crystals of extraordinary size. Some of the largest single crystals ever recorded are microcline.
- Chiefly from
- Colorado, United StatesKarelia, RussiaBrazilMadagascar
Safety
No hazard from handling.
Where it comes from
Common. Pegmatite mining for feldspar, mica and lithium supplies most specimen material as a by-product.
Historical use
Chemically identical to orthoclase and distinguished only by its ordering and symmetry, which is why the two were confused for a long time. A microcline crystal from Karelia measuring around fourteen metres is among the largest crystals of anything known.
Recorded as history and attributed where possible. That a stone was used for something establishes that people used it, not that it worked.
Worth knowing
Microcline and orthoclase have exactly the same formula. What separates them is how tidily the aluminium and silicon atoms are arranged, which depends on how slowly the mineral cooled: fast cooling gives the disordered form, slow cooling gives the ordered one. Two minerals, one composition, distinguished by patience.
This is a useful thing to hold on to when reading claims about what a stone's structure does. The structural difference here is real, measurable and consequential enough to justify two separate species names — and it is entirely invisible to the eye and to the hand.
Identity checked against IMA-CNMNC master list, June 2025.