EOSC 118 Lecture Notes - Lecture 20: Pegmatite, Tourmaline, Intrusive Rock
18 Nov 2016
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Document Summary
Premier rock type for finding large high quality gemstones (with exception of diamond) Pegmatite gemstones occur in specific locations within a pegmatite called pockets. Pegmatites supply the best tourmaline, topaz, and beryl. Hosts for rare metal deposits including li, ta, nb, and sn. Term pegmatite used as a descriptor for igneous rocks with large crystal sizes. Base composition similar to granite but with significant enrichment in rare elements. 3 main minerals are feldspare, quartz, and mica. Rare elements that are commonly enriched in pegmatites: be, li, cs, ta nb, y, f, rb, sn, ga, b. 3 most common pegmatite gems: tourmaline, topaz, and spodumene. Barren magma do not generate highly fractionated pegmatites. Classification of pegmatites type of rare element enrichment medium t, low p) Rare element pegmatites tend to produce the most gemstones. Usually form as sheets, pods, lenses, or cigar-shaped bodies in large plutonic bodies. Large crystals due to large amount of water in the magma.
