Properties
| Category | Tectosilicate minerals |
|---|---|
| Formula | SiO2 (silicon dioxide) |
| Crystal system | Trigonal (quartz), Monoclinic (moganite) |
| Color | Black and white; red to brown with black or white (sardonyx) |
| Cleavage | None |
| Fracture | Uneven, conchoidal |
| Mohs scale hardness | 6.5–7 |
| Luster | Vitreous, silky |
| Streak | White |
| Diaphaneity | Translucent |
| Specific gravity | 2.55–2.70 |
From the Wikipedia article
Onyx is a typically black-and-white banded variety of agate, a silicate mineral. The bands can also be monochromatic with alternating light and dark bands. Sardonyx is a variety with red to brown bands alternated with black or white bands. The name "onyx" is also frequently used for level-banded (parallel-banded) agates, but in proper usage it refers to color pattern not band structure. Onyx, as a descriptive term, has also been incorrectly applied to parallel-banded varieties of alabaster, marble, calcite, obsidian, and opal, and misleadingly to materials with contorted banding, such as "cave onyx" and "Mexican onyx".
Source
Source record: crystal-compendium/sardonyx/minerals.json. Fetched from English Wikipedia by the operator 2 October 2026.
https://en.wikipedia.org/wiki/Onyx — revision id 1369833689. Text and properties from Wikipedia, licensed CC BY-SA 4.0.