Euclaseis aberylliumaluminiumhydroxidesilicatemineral (BeAlSiO4(OH)). It crystallizes in themonocliniccrystal systemand is typically massive to fibrous as well as in slender prismatic crystals. It is related toberyl(Be3Al2Si6O18) and other beryllium minerals. It is a product of the decomposition of beryl inpegmatites.[4]
| Euclase | |
|---|---|
 | |
| General | |
| Category | Nesosilicate |
| Formula (repeating unit) | BeAlSiO4(OH) |
| IMA symbol | Ecs[1] |
| Strunz classification | 9.AE.10 |
| Crystal system | Monoclinic |
| Crystal class | Prismatic (2/m) (sameH-M symbol) |
| Space group | P21/a |
| Unit cell | a = 4.763, b = 14.29 c = 4.618 [Å]; β = 100.25°; Z = 4 |
| Identification | |
| Color | Colorless, white, pale green to deep yellowish green, greenish blue, pale blue to deep blue, and light red |
| Crystal habit | Prismatic crystals |
| Cleavage | Perfect, perfect on {010}, imperfect on {110} {001} |
| Fracture | Conchoidal |
| Tenacity | Brittle |
| Mohs scalehardness | 7.5 |
| Luster | Vitreous |
| Streak | White |
| Diaphaneity | Transparent, translucent |
| Specific gravity | 2.99 - 3.1 |
| Optical properties | Biaxial (+) |
| Refractive index | nα= 1.652 nβ= 1.655 nγ= 1.671 |
| Birefringence | δ = 0.019 |
| Pleochroism | May be marked in shades of deep blue |
| 2V angle | 50° |
| Dispersion | r > v |
| References | [2][3][4] |
Euclase crystals are noted for their blue color, ranging from very pale to dark blue. The mineral may also be colorless, white, or light green.Cleavageis perfect, parallel to theclinopinacoid,and this suggested toRené Just Haüythe name euclase, from the Greekεὖ,easily, andκλάσις,fracture. The ready cleavage renders the crystals fragile with a tendency to chip, and thus detracts from its use for personal ornament. When cut, it resembles certain kinds of beryl andtopaz,from which it may be distinguished by its specific gravity (3.1). Its hardness (7.5) is similar to beryl (7.5 - 8), and a bit less than that of topaz (8).[5] It was first reported in 1792 from theOrenburgdistrict in the southernUrals,Russia,where it is found with topaz andchrysoberylin the gold-bearing gravels of the Sanarka (nowadays probably,Sakmara River,Mednogorsk district,Orenburgskaya Oblast'). Itstype localityis Ouro Prêto,Minas Gerais,Southeast Region,Brazil,[3]where it occurs with topaz. It is found rarely in themica-schistof theRaurisin the Austrian Alps.
References
edit- ^Warr, L.N. (2021)."IMA–CNMNC approved mineral symbols".Mineralogical Magazine.85(3):291–320.Bibcode:2021MinM...85..291W.doi:10.1180/mgm.2021.43.S2CID235729616.
- ^Euclase data on Webmineral
- ^abEuclase on Mindat.org with location data
- ^abEuclase in the Handbook of Mineralogy, Mineral Data Publishers PDF
- ^Chisholm, Hugh,ed. (1911)..Encyclopædia Britannica(11th ed.). Cambridge University Press.
