igneous
Granitic Pegmatite with Tourmaline and Sphalerite
Pegmatite containing Schorl (NaFe3Al6(BO3)3Si6O18(OH)4) and Sphalerite ((Zn,Fe)S)
Hardness: 6-7.5 (variable); Color: White matrix (quartz/feldspar) with black elongated schorl crystals and green/dark metallic sphalerite; Luster: Vitreous to resinous; Structure: Large, interlocking crystals typical of pegmatitic textures.
- Hardness
- 6-7
- Luster
- Vitreous to resinous
Identified More igneous →
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Physical properties
Hardness: 6-7.5 (variable); Color: White matrix (quartz/feldspar) with black elongated schorl crystals and green/dark metallic sphalerite; Luster: Vitreous to resinous; Structure: Large, interlocking crystals typical of pegmatitic textures.
Formation & geological history
Formed during the final stages of a magma chamber's crystallization, where water-rich fluids allow for the growth of massive crystals. These typically date to various Orogenic cycles depending on local geology.
Uses & applications
Primarily of value to geological collectors and museums; pegmatites are also sources of rare earth elements, lithium, and gemstones.
Geological facts
The label in the image mentions 'Sphalerite', a major ore of zinc. Pegmatites are famous for producing the largest individual crystals ever found on Earth due to the unique fluid dynamics of their formation.
Field identification & locations
Identify in the field by the exceptionally large crystal grain size (pegmatitic texture) and the presence of elongated black tourmaline (schorl) needles in a white quartz/feldspar matrix.
