Yugawaralite, 1.01 cts. Photo © Joel E. Arem, PhD, FGA. Used with permission.
Yugawaralite is a very rare colorless to pinkish zeolite mineral. Little facetable material exists, so a cut yugawaralite would be a prized addition to a gem collection.
| Data | Value |
|---|---|
| Name | Yugawaralite |
| Is a Variety of | Zeolite |
| Crystallography | Monoclinic: crystals tabular and very flat. |
| Refractive Index | 1.495-1.504 |
| Colors | Colorless, white, pinkish. |
| Luster | Vitreous. |
| Hardness | 4.5 |
| Fracture | Conchoidal |
| Specific Gravity | 2.23-2.25 |
| Birefringence | 0.009 |
| Cleavage | Imperfect |
| Dispersion | Weak. |
| Luminescence | None reported. |
| Luminescence Present | No |
| Transparency | Transparent. |
| Absorption Spectrum | None. |
| Formula | CaAl2Si6O16 · 4H2O. |
| Pleochroism | None. |
| Optics | a = 1.495; β = 1.497; γ = 1.504. Biaxial (+). |
| Optic Sign | Biaxial + |
| Etymology | Named after its type locality, Yugawara Hot Spring, Japan. |
| Occurrence | In veins and crystals in volcanic rocks (Japan) and in huge crystals in breccia cavities (India). |
Yugawaralite from Mumbai, India, from the collection of the A. E. Seaman Mineral Museum, Houston, Michigan. Photo by Chris857. Licensed under CC By-SA 3.0.
The Kandivali Quarry near Mumbai, India has produced superb, well-formed colorless and transparent crystals close to the literature values for yugawaralite. A few faceted gems have been cut from this exceptional and extremely rare material.
Yugawaralites have both pyroelectric and piezoelectric properties. This means they generate electricity when heated and placed under pressure, respectively.
Transparent, tabular yugawaralite crystals, the longest measure 0.7 mm. Malad Quarry (Kandivali Quarry), Malad, Ward 38, Mumbai (Bombay), Mumbai District (Bombay District), Maharashtra, India. Photo by Gianfranco Ciccolini. Public Domain.
Scientists have synthesized yugawaralites as well as other zeolites for chemical and mineralogical research. However, there is no known jewelry use for this synthetic material.
None known.
Japan, notably Honshu Island, produces gemmy material. Yugawara Hot Spring, Kanagawa Prefecture is the type locality for yugawaralite.
India, most notably the Kandivali Quarry, produces small amounts of facetable material.
Other notable crystal sources include the following:
Yugawaralite (picture width: 20 x 10 mm), Cirque de Cilaos, Piton des Neiges, Réunion Island. Photo by Michel Poullaouec. Public Domain.
The Kandivali Quarry can produce gem-quality crystals up to 3 cm long.
You’re more likely to find yugawaralites, if at all, in gem collections than jewelry collections. If used in jewelry, these stones would require protective settings and occasional wear only. Their hardness of 4.5 means they can be scratched very easily, and their very brittle tenacity means they’re more likely than most gems to fracture from impact. Clean these gemstones only with a warm damp cloth, mild detergent, and soft brush. For more care recommendations, consult our gemstone jewelry cleaning guide.
Yugawaralite from Toi-cho, Shizuoka Province, Japan, on display at the Natural History Museum, Berlin. Photo by Alice Chodura. Licensed under CC By-SA 3.0.
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