Blue Sodalite a tectosilicate mineral


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blue sodalite two pieces of rich royal blue tectosilicate mineral

Mineral Group  silicate
Composition  complex aluminosilicate of sodium with chlorine, Na8Cl2(AlSiO4)6
dimension (cm)  2.5x2x1
weight (g)  13
from Wikipedia – Sodalite is widely used as an ornamental gemstone.
Discovered in 1811 in the Ilimaussaq intrusive complex in Greenland, sodalite did not become important as an ornamental stone until 1891 when vast deposits of fine material were discovered in Ontario, Canada.
Sodalite has been known since early times; it is found fairly frequently in the ruins of the Bolivian city of Tihuanaca. However, it was defined as a distinct mineral only in 1811 by the British mineralogist, T. Thomson. Sodalite most commonly forms compact or granular aggregates, and on rarer occasions cleavable crystals, often twinned. Usually it is found in igneous rocks poor in silicon dioxide, such as nepheline syenites. Quite frequently it is an important rock-forming mineral, where it is often a substitute for feldspar. This is why, in petrography, it is referred to as the feldspar replacer.
The main deposits are at Ditrau (Romania), Serra de Monchique in Portugal, volcanic formations on Monte Somma (Vesuvius), Monti Albani near Rome, Rieden in Germany, Miass in the Urals (Russia), Kangerdluarsuk in Greenland, Ontario in Canada, the USA, Cerro Sapo in Bolivia, and Burma. In microscopic form, sodalite occurs in various trachytes, phonolites and basalts. It is used today as a semiprecious stone, usually ground to lenticular or tabular shape. Only the darker sodalites are popular, because they resemble lazurite in richness and shade of colour. The Canadian sodalites meet these requirements, and sometimes also those found in the USA and the Urals.
Sodalite often occurs with lazurite and possibly with other related aluminosilicates, of which there are quite a number. The best known of them is hauynite, named in honour of the founder of scientific crystallography, R. J. Hauy. As distinct from sodalite, it does not contain chlorine but sulphur and an admixture of calcium. It also has a higher degree of hardness and specific gravity than sodalite.

Additional information

Weight 13 g
Dimensions 2.5 x 2 x 1 cm