gemstone
Blue-green tourmaline (likely indicolite)
Elbaite tourmaline, Na(Li1.5Al1.5)Al6(BO3)3Si6O18(OH)4
AI-generated identification · may be incorrectHardness 7–7.5 Mohs; blue-green color, vitreous luster, and commonly prismatic/trigonal crystals with strong lengthwise striations and indistinct cleavage. The specimen appears to be a rough, partly fractured crystal with dark matrix or surface alteration.
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Physical properties
Hardness 7–7.5 Mohs; blue-green color, vitreous luster, and commonly prismatic/trigonal crystals with strong lengthwise striations and indistinct cleavage. The specimen appears to be a rough, partly fractured crystal with dark matrix or surface alteration.
Formation & geological history
Forms in lithium-rich granitic pegmatites through late-stage hydrothermal crystallization, commonly during the Precambrian to Mesozoic depending on locality. Typical sources include Brazil, Afghanistan, Pakistan, Madagascar, Nigeria, and the United States.
Uses & applications
Transparent material is cut for jewelry; opaque or fractured pieces are sold as mineral specimens and used for lapidary carving. Tourmaline is also valued for its piezoelectric and pyroelectric properties.
Geological facts
Indicolite is the blue variety of elbaite; green-blue zoning is common and can be diagnostic of pegmatite growth conditions. Tourmaline crystals often develop triangular cross-sections and longitudinal grooves.
Field identification & locations
Identify by its blue-green hue, vitreous sheen, hardness, striated prismatic form, and lack of prominent cleavage; a gemological test is needed to distinguish it from beryl or apatite. Look for associated quartz, albite, lepidolite, or feldspar.
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