Tephrite
Tephrite is a dark, fine-grained volcanic rock that contains feldspathoid minerals such as nepheline or leucite. It can resemble basalt in hand sample.
.jpg?width=760)
Tephrite properties at a glance
| Type | Igneous Rocks |
|---|---|
| Chemical formula | Feldspathoid-bearing mafic volcanic rock |
| Mohs hardness | 6 |
| Luster | dull |
| Streak | Gray to dark gray |
| Cleavage | None to variable by phenocrysts |
| Fracture | Uneven to conchoidal |
| Specific gravity | 2.85 |
| Transparency | opaque |
| Common colors | Dark gray, Black, Brown, Gray, Greenish black |
| Rarity | uncommon |
Geology & background
Forms from silica-undersaturated mafic lava containing plagioclase, pyroxene, and feldspathoid minerals instead of abundant quartz.
Tephrite helps geologists recognize silica-undersaturated volcanic provinces and alkaline magmas.
How to identify Tephrite
- 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.
Where Tephrite is found
Reported from multiple igneous terrains worldwide; verify locality against specimen provenance when available.
How much is Tephrite worth?
| Entry-level specimen | $1 |
|---|---|
| Typical collector specimen | $10 |
| Premium specimen | $75+ |
Tephrite is usually valued for teaching, field context, locality, texture, color, mineral content, or unusually attractive specimens rather than high gem value.
Common uses
- Field identification
- Volcanic rock comparison
- Education
- Collector specimens
Interesting facts
- Tephrite is silica-undersaturated and typically lacks quartz.
- Leucite or nepheline may be present as feldspathoid minerals.
- It can be visually difficult to separate from basalt without context.
Care & safety
Tephrite can vary in toughness, porosity, vesicles, glass content, and weathering depending on cooling history and mineral mix.
Avoid inhaling dust. Do not cut, grind, or polish unknown igneous rocks without eye protection and a properly rated respirator.
.jpg?width=320)
_3.jpg?width=320)
