RocksdayNepheline vs Orthoclase
How to tell them apart
A silica-poor 'feldspathoid' found in rocks that formed without enough silica for quartz.
Photo: Andrew Silver, USGS, Public domain
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
- Feldspar has good cleavage faces.
Side by side
| Property | Nepheline | Orthoclase |
|---|---|---|
| Type | Mineral | Mineral |
| Mohs hardness | 5.5–6 | 6 |
| Luster | Greasy to vitreous | Vitreous |
| Streak | White | White |
| Colors | Gray, White, Brown | Pink, White, Orange |
| Crystal system | Hexagonal | Monoclinic |
| Specific gravity | 2.55–2.66 | 2.55–2.63 |
| Formula | (Na,K)AlSiO₄ | KAlSi₃O₈ |
| Found in | Bancroft, Ontario; Kola Peninsula, Russia | Granites worldwide; Karlovy Vary, Czech Republic |
Properties that are the same for both are grayed out.
How to identify nepheline
- Gray, greasy-looking grains.
- Never occurs with quartz.
- Hardness about 6, poor cleavage.
Crystal system: Hexagonal
Full Nepheline 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
Could you tell them apart from a blurry close-up?
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