igneous
Quartz with Tourmaline and Iron Staining
Silicon Dioxide (SiO2) with Schorl (NaFe2+3Al6(Si6O18)(BO3)3(OH)3OH)
Hardness: 7 (Quartz) and 7-7.5 (Tourmaline). Color: Clear/white matrix, black crystals, orange-brown staining. Luster: Vitreous to greasy. Crystal Structure: Hexagonal/Trigonal. Cleavage: Indistinct/Conchoidal. Specific Gravity: 2.65-3.1.
- Hardness
- 7 (Quartz) and 7-7
- Color
- Clear/white matrix, black crystals, orange-brown staining
- Luster
- Vitreous to greasy
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Physical properties
Hardness: 7 (Quartz) and 7-7.5 (Tourmaline). Color: Clear/white matrix, black crystals, orange-brown staining. Luster: Vitreous to greasy. Crystal Structure: Hexagonal/Trigonal. Cleavage: Indistinct/Conchoidal. Specific Gravity: 2.65-3.1.
Formation & geological history
Formed in an igneous pegmatite or hydrothermal vein environment where mineral-rich fluids cooled slowly, allowing large crystals to form. The orange staining is likely limonite or goethite from iron oxidation.
Uses & applications
Used primarily as decorative collector specimens. Quartz is used in electronics and glass-making; Tourmaline is used in jewelry and for its pyroelectric properties.
Geological facts
Black tourmaline, also known as Schorl, is the most common variety of tourmaline and was known as early as the 1400s in Saxony, Germany. The orange crust is a common weathering product of iron-bearing minerals.
Field identification & locations
Identify by its hardness (will scratch glass), the vitreous luster of the clear quartz, and the elongated, vertically striated black crystals typical of tourmaline schorl. Commonly found in granitic pegmatite regions.
