RocksdayMicrocline vs Orthoclase
To tell Microcline from Orthoclase: Orthoclase is the monoclinic potassium feldspar; the grid twinning of microcline shows only under crossed polarizers.
The common potassium feldspar of granite pegmatites. Green microcline is amazonite. By eye it looks like orthoclase.
Photo: Robert M. Lavinsky, CC BY-SA 3.0
A potassium feldspar and one of the most common minerals in granite, where it forms the pink or cream-colored blocks.
Photo: Didier Descouens, CC BY-SA 4.0
Key differences
- Orthoclase is the monoclinic potassium feldspar; the grid twinning of microcline shows only under crossed polarizers.
Side by side
| Property | Microcline | Orthoclase |
|---|---|---|
| Type | Mineral | Mineral |
| Mohs hardness | 6–6.5 | 6 |
| Luster | Vitreous to pearly | Vitreous |
| Streak | White | White |
| Colors | Pink, White, Green, Gray | Pink, White, Orange |
| Crystal system | Triclinic | Monoclinic |
| Specific gravity | 2.54–2.63 | 2.55–2.63 |
| Formula | KAlSi₃O₈ | KAlSi₃O₈ |
| Found in | Pegmatites in Colorado; Minas Gerais, Brazil | Granites worldwide; Karlovy Vary, Czech Republic |
Properties that are the same for both are grayed out.
How to identify microcline
- Blocky pink, white or green crystals with two cleavages near 90°.
- Hardness about 6 — scratches glass with difficulty.
- Green pieces are amazonite. Pink and white ones cannot be separated from orthoclase without a microscope.
Crystal system: Triclinic
Full Microcline guide →How to identify orthoclase
- Blocky pink to cream crystals in granite.
- Two cleavages meeting at a right angle — flat, shiny faces.
- Hardness 6 — scratches glass with effort.
- No fine parallel striations (unlike plagioclase).
Crystal system: Monoclinic
Full Orthoclase guide →More comparisons
Frequently asked questions
What is the difference between microcline and orthoclase?
Microcline is a mineral (KAlSi₃O₈) with a Mohs hardness of 6–6.5 and a vitreous to pearly luster, usually pink, white, green or gray. Orthoclase is a mineral (KAlSi₃O₈) with a Mohs hardness of 6 and a vitreous luster, usually pink, white or orange.
How can you tell microcline from orthoclase?
Orthoclase is the monoclinic potassium feldspar; the grid twinning of microcline shows only under crossed polarizers.
Could you tell them apart from a blurry close-up?
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