Identification guide · Igneous Rocks
How to Identify Tephrite
Tephrite is usually dark gray, black, and brown with a dull luster and is opaque. 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 gray to dark gray. It is most often confused with Basalt, Basaltic Andesite, and Trachyte; the tests below separate them.
Tephrite identification checklist
| Color | Dark gray, Black, Brown, Gray, Greenish black | Look at a clean, dry surface in daylight. Color zoning, banding or spots are as diagnostic as the hue. |
|---|---|---|
| Luster | Dull | Compare a fresh surface with glass and metal; this luster is softer than either. |
| Transparency | Opaque | 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 | Gray to dark gray | Drag a corner across unglazed porcelain (the back of a bathroom tile) and check the powder color. |
| Cleavage | None to variable by phenocrysts | |
| Fracture | Uneven to conchoidal | Broken surfaces show smooth, curved, shell-like scoops. |
| Specific gravity | 2.85 | Ordinary rock-like heft (specific gravity about 2.85), similar to quartz. |
Tephrite 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. Tephrite vs Basalt →
Both sit near Mohs 6, so a scratch test alone will not separate them. Lean on luster, streak and heft instead. Tephrite vs Basaltic Andesite →
Both sit near Mohs 6, so a scratch test alone will not separate them. Lean on luster, streak and heft instead. Tephrite vs Trachyte →
Both sit near Mohs 6, so a scratch test alone will not separate them. Lean on luster, streak and heft instead.
Field tips
- Look for dark, fine-grained volcanic texture that resembles basalt.
- Visible pale leucite or nepheline spots can support tephrite.
- Tephrite generally lacks quartz.
- Locality and geologic context are important because hand-sample photos can be ambiguous.
Tephrite identification FAQ
How can you tell if a rock is Tephrite?
Check the color (dark gray, black, brown, and gray), the dull luster, a Mohs hardness of 6 and a gray to dark gray streak. Photographing it with the StoneSnap app gives a match in seconds.
What is the hardness of Tephrite?
Tephrite 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 Tephrite and Basalt?
Tephrite (Mohs 6, dull luster) and Basalt (Mohs 6, dull luster) look alike, but hardness, streak and heft usually separate them. See the full Tephrite vs Basalt comparison for a side-by-side table.
Is Tephrite worth anything?
Entry-level Tephrite specimens sell for around $1, typical collector pieces about $10, and premium examples $75 or more depending on size, quality and locality.
What color is Tephrite?
Tephrite is most often dark gray, black, brown, and gray. Color varies with impurities and locality, so confirm with hardness and luster rather than color alone.
