User:Tiagomagno/sandbox

Jimthompsonite is part of the common triple chain silicates along with clinojimthompsonite and chesterite. They were described in 1977 by Burham and Veblen. They attracted great mineralogical attention because they were the first examples of new chain silicate structures among a large group known as byopyriboles that came from the words biotite, pyroxene, and amphiboles. Dr. James B. Thompson, Jr. Postulated the existence if the new biopyroles in 1970. The theory proved correct when jimthompsonite, clinojimthompsonite and chesterite were discovered in Vermont. The new minerals are found intergrown with the amphiboles anthophylite and cumingtonite in sprays up to 5 cm long. They are all colorless to pale pinkish-brown and transparent. As for pyroxene and amphiboles, the type of chain structure dictates the angle between the two distinctive cleavages. The cleavages of jimthompsonite are at 142 degrees and 38 degrees, and 135 degrees and 45 for chesterite, Compared to the cleavage angles of pyroxene at about 94 degrees and 86 degrees and amphibole about 124 and 56 degrees. Composition The chemical formula of jimthompsonite is(Mg, Fe++) 5Si6O 16(OH) 2. Veblen and Durham determined the percentages of jimthompsonite as follow: - Magnesium 14.71% Mg 24. 40% MgO. - Iron 11.27 % Fe 14.50 % FeO. - Silicon 27.20 % Si 58.20 % SiO2. - Hydrogen 0.33% H2.91% H2O. -Oxygen 46.49% O. Some of the other characteristics of jimthompsonite are that it has an orthorhombic crystal system Dipyramidal IH-M symbol (2/m 2/m 2/m), space group: Pbca. It has a perfect cleavage, its colorless pink brown with a density of 3.03g/cm3 and hardness of 2-2.5 Gypsum or finger nail. White streak and silky-pearly luster.

Origin It is found in the Carleton talc quarry, near Chester, Windsor Co, Vermont, USA. The name triple chain silicate comes from a wide complex chain structure as Silicon being the most dominant element in its composition. It was named for James Burleigh Thompson, Jr. (1921- ), petrologist of Harvard University, Cambridge, Massachusetts, USA.