Andradite is a mineral , a silicate from the group of pomegranates . Named after the Brazilian mineralogist Jose Bonifacio de Andrada e Silva ( port. José Bonifácio de Andrade e Silva , 1763-1838).
| Andradit | |
|---|---|
 Andradite crystals , 7cm. Sinerechensk deposit, Primorye . Photo: V. Slyotov , c http://mindraw.web.ru | |
| Formula | Ca 3 Fe 2 Si 3 O 12 or 3CaO · Fe 2 O 3 · 3SiO 2 |
| Physical properties | |
| Colour | Black, tan, red, greenish yellow, gray |
| Trait color | White |
| Shine | Glass |
| Transparency | Transparent, translucent |
| Hardness | 6.5-7 |
| Cleavage | Not |
| Density | 3.7-4.1 g / cm³ |
| Syngonia | Cubic (Planaxial) |
| Refractive index | 1,888 |
A relatively widespread representative of the group of garnets is found in the form of separate well-formed crystals of a rhombic dodecahedral or tetragontrioctahedral shape, with a characteristic hatching on the faces. Crystals form irregular splices, drusen , crystalline crusts in cracks and voids of rocks. Also in the form of veins, individual grains and interspersed.
Content
Properties
The percentage composition: CaO - 33.10, Fe 2 O 3 - 31.43, SiO 2 - 35.47. Cleavage is absent, sometimes separate . The fracture is uneven to semi-awkward. It is difficult to dissolve in concentrated hydrochloric acid . Weakly magnetic , fuses under a soldering tube into a magnetic bead .
Varieties
Depending on impurities, color and gloss are distinguished:
- demantoid (green);
- topazolite (yellow-green);
- colophonite (reddish brown, tar gloss);
- yellowing (light green);
- melanite (black, contains TiO 2 ).
Origin
Along with almandine, it is the most common representative of the group of pomegranates in the Earth's crust . Andradite is formed during contact-metasomatic and metamorphic processes, occurs in skarns in association with magnetite , epidote , chlorites , pyrite , quartz , calcite , etc.
Practical Importance
Ordinary ordinary andradite has no practical use (with the exception of a rare precious variety - the demantoid ), but in the form of well-formed crystals , friends and crystal brushes, it is popular as a beautiful decorative and collection material.
Links
- Andradit in Geovikipedia
- Andradit on Kristallov.NET
- Andradit in the webmineral.com database
- Andradit Descriptions, deposits and many photos