Rhyolite
Rhyolite is classified as a volcanic rock, characterized by a porphyritic texture where crystals are scattered within a nearly glassy matrix. Previously known as quartz porphyry, it is now called rhyolite (meaning "flow rock") due to its flow banding structure (the English name "Rhyolite" was coined in 1860).
Appealing for the unique patterns created by flow structures and spherulites
Basic Information
| English Name | Rhyolite |
|---|---|
| Japanese Name | Ryumon-gan |
| Composition | Quartz, plagioclase, hornblende, pyroxene, mica, etc. |
| Classification | Volcanic rock |
| Hardness | 5–7 |
| Specific Gravity | Variable |
| Transparency | Opaque (generally) |
Characteristics & Varieties
- Banded Rhyolite: Rhyolite with distinct flow banding structures.
- Spherulitic Rhyolite: Contains spherulites—rounded clusters of crystals. In the suiseki (viewing stone) world, these are sometimes called "peony stone" or "chrysanthemum stone."
- Lithoidite: A term for rhyolite that is more stony in matrix composition compared to porphyritic types.
- Patterned Stones: Due to the oxidation of iron within the matrix, these exhibit unique patterns; those resembling landscapes or paintings are called "landscape stones" or "picture stones."
Trade Names, Treatments, & Related Information
Trade/Commercial Names: Flower Jasper, Picture Jasper, Landscape Jasper. Because it is opaque, it is often misidentified as Jasper, but it is frequently not true jasper.
Treatments: In rare cases, filling treatments may be applied to hollow spherulite areas.
Related Info: In the circular areas of spherulites, one can often observe crystal structures radiating from the center.
Related Info: When rhyolitic lava solidifies rapidly, it leaves no time for crystallization, resulting in amorphous Obsidian.
Related Info: Mexican opal cut with its host rock (rhyolite) is known as Cantera opal (Opal).
Note: Being opaque, it is prone to misidentification, and trade names often take precedence. Understanding the "base rock" helps provide accurate explanations.