Metamorphic
Feldspar-rich Quartzite
Feldspathic Quartzite (Metamorphosed Sandstone)
Hardness: 6-7 (Mohs scale); Color: Pinkish-tan to white with grey inclusions; Luster: Vitreous to pearly on cleavage planes; Crystal structure: Non-foliated, granoblastic texture; Cleavage: Two directions at nearly 90 degrees in feldspar crystals, none in quartz; Specific gravity: 2.6 - 2.8.
- Hardness
- 6-7 (Mohs scale)
- Color
- Pinkish-tan to white with grey inclusions
- Luster
- Vitreous to pearly on cleavage planes
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Physical properties
Hardness: 6-7 (Mohs scale); Color: Pinkish-tan to white with grey inclusions; Luster: Vitreous to pearly on cleavage planes; Crystal structure: Non-foliated, granoblastic texture; Cleavage: Two directions at nearly 90 degrees in feldspar crystals, none in quartz; Specific gravity: 2.6 - 2.8.
Formation & geological history
Formed through the regional metamorphism of arkosic sandstone (sandstone rich in feldspar). High heat and pressure Recrystallized the sand grains into a dense, interlocking matrix. Geologically found in mountain belts and ancient shield areas ranging from hundreds of millions to billions of years old.
Uses & applications
Used primarily as decorative stone, crushed aggregate for road construction, and ballast. Certain attractive specimens are used in lapidary work or landscape design. Industrially, it can be a source of silica and alumina.
Geological facts
Quartzite is so tough that it usually breaks through the quartz grains rather than around them. The pink coloration in this specimen is likely due to potassium feldspar (orthoclase) or slight iron oxide staining.
Field identification & locations
Identify in the field by its hardness (it will scratch glass easily) and its sugary, crystalline texture. It is commonly found in eroded mountain ranges like the Appalachians or the Rockies. For collectors, look for high feldspar content (pinkish hues) and large crystal faces.
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