Dumortierite - a mineral , aluminum borosilicate. The crystal structure of the island type. Discovered in 1881 in the French Alps and named after the French paleontologist E. Dumortier ( French: Eugène Dumortier ; 1803-1873).
| Dumortierite | |
|---|---|
 Dumortierite from Madagascar | |
| Formula | Al 7 (BO 3 ) (SiO 4 ) 3 O 3 |
| Physical properties | |
| Color | Blue, Violet Blue, Reddish Brown |
| Trait color | bluish |
| Shine | Glass |
| Transparency | Opaque |
| Hardness | 7 |
| Cleavage | average |
| Kink | uneven |
| Density | 3.26 - 3.41 g / cm³ |
| Syngonia | Rhombic |
| Refractive index | 1,686 - 1,723 |
Crystals are very rare, usually forming dense radiant or fibrous aggregates. Dispersion is absent. Strong pleochroism (black - red-brown - brown). No luminescence . When calcined with cobalt nitrate, it acquires a blue color. Slowly soluble in HF.
It can be confused with azurite , lapis lazuli , sodalite . Close intergrowths of this mineral with dense quartz are known.
Content
- 1 production sites
- 2 Application
- 3 Chemical composition
- 4 Processing
- 5 Literature
- 6 References
Mining Places
It is found in Brazil , Russia, Canada , Madagascar , Sri Lanka , Namibia , USA ( California , Nevada , in pegmatite dikes in Manhattan ), France (in gneisses near Lyon and Bion ), Australia, Poland ( Silesia ).
Application
Used in the manufacture of high-grade electrical porcelain . It used to be used in jewelry . A popular collectible mineral.
Chemical Composition
The chemical composition of dumortierite is interesting in that boron is included in it. Dumortierite belongs to borosilicates along with such minerals as corneurupin, prismatine, harkerite, granditierite, holtite, etc.
Dumortierite is formed in pegmatites and boron-rich metamorphic rocks, where it is considered the most common borosilicate after the minerals of the tourmaline group. Dumortierite contains less than 2% of boron, so it cannot act as ore of this element.
Processing
Figurines and cabochons of beautiful blue are cut from dumortierite aggregates. In the case of dumortierite, cuts typical of other minerals are practically not used, since suitable specimens are rarely found. But in those rare cases when dumortierite is still faceted, the results exceed all expectations.
Literature
- Schumann V. The world of stone. Precious and ornamental stones. - M .: Mir, 1986. P.174.