Identification guide · Silicate Minerals
How to Identify Orthoclase
Orthoclase is usually colorless, white, and cream with a vitreous luster and is translucent. It has a Mohs hardness of 6. It is about as hard as window glass: a knife barely marks it, while a steel file (Mohs 6.5) will. Its streak is white. It is most often confused with Leucite, Nepheline, and Albite; the tests below separate them.
Orthoclase identification checklist
| Color | Colorless, White, Cream, Pink, Yellow | Look at a clean, dry surface in daylight. Color zoning, banding or spots are as diagnostic as the hue. |
|---|---|---|
| Luster | Vitreous | Fresh surfaces shine like glass; a dull surface usually means weathering, so chip or wet a corner. |
| Transparency | Translucent | Hold a thin edge up to a bright light and note whether light passes through. |
| Mohs hardness | 6 | It is about as hard as window glass: a knife barely marks it, while a steel file (Mohs 6.5) will. |
| Streak | White | Drag a corner across unglazed porcelain (the back of a bathroom tile) and check the powder color. |
| Cleavage | Perfect on {001}, good on {010} | |
| Fracture | Uneven to conchoidal | Broken surfaces show smooth, curved, shell-like scoops. |
| Specific gravity | 2.56 | Ordinary rock-like heft (specific gravity about 2.56), similar to quartz. |
| Crystal system | Monoclinic |
Extra tests for Orthoclase
Glass check. Orthoclase shares a glassy luster and conchoidal fracture with man-made glass. Glass sits near Mohs 5.5 and often contains round gas bubbles, so a hardness test and a hand lens separate them.
Orthoclase look-alikes and how to tell them apart
Both sit near Mohs 6, so a scratch test alone will not separate them. Lean on luster, streak and heft instead. Orthoclase vs Leucite →
Both sit near Mohs 6, so a scratch test alone will not separate them. Lean on luster, streak and heft instead. Orthoclase vs Nepheline →
Both sit near Mohs 6, so a scratch test alone will not separate them. Lean on luster, streak and heft instead. Orthoclase vs Albite →
Both sit near Mohs 6, so a scratch test alone will not separate them. Lean on luster, streak and heft instead. Orthoclase vs Microcline →
Field tips
- Look for blocky cream, pink, or colorless crystals with two cleavage directions at right angles.
- Orthoclase has a hardness of 6 and a vitreous luster, often with a pearly sheen on cleavage faces.
- It is hard to separate from microcline by eye; twinning and optical tests confirm the species.
Orthoclase identification FAQ
How can you tell if a rock is Orthoclase?
Check the color (colorless, white, cream, and pink), the vitreous luster, a Mohs hardness of 6 and a white streak. Photographing it with the StoneSnap app gives a match in seconds.
What is the hardness of Orthoclase?
Orthoclase has a Mohs hardness of 6. It is about as hard as window glass: a knife barely marks it, while a steel file (Mohs 6.5) will.
What is the difference between Orthoclase and Leucite?
Orthoclase (Mohs 6, vitreous luster) and Leucite (Mohs 5.75, vitreous luster) look alike, but hardness, streak and heft usually separate them. See the full Orthoclase vs Leucite comparison for a side-by-side table.
Is Orthoclase worth anything?
Entry-level Orthoclase specimens sell for around $5, typical collector pieces about $35, and premium examples $250 or more depending on size, quality and locality.
What color is Orthoclase?
Orthoclase is most often colorless, white, cream, and pink. Color varies with impurities and locality, so confirm with hardness and luster rather than color alone.
