Quartzite

Discover quartzite, a very hard metamorphic rock formed from sandstone.

Overview

Quartzite is a metamorphic rock formed from the recrystallization of sandstone. It is composed almost entirely of quartz and is extremely hard and durable. Quartzite is resistant to weathering and is used as a building stone and decorative material.

What Is Quartzite?

Definition: Quartzite is a metamorphic rock formed from the recrystallization of sandstone. The original sand grains and cement are recrystallized into interlocking quartz crystals, creating an extremely hard, durable rock. Composition: Almost entirely quartz (SiO₂), with: - Original sand grains recrystallized - Cement recrystallized - Sometimes minor amounts of other minerals Color: Usually white, gray, or tan. Can be pink, red, or other colors if the original sandstone contained iron oxides or other minerals. Texture: Crystalline, with interlocking quartz crystals. Very hard and compact.

Formation and Occurrence

How It Forms: Quartzite forms from the metamorphism of sandstone: - Temperature: 400-700°C - Pressure: Moderate to high - Recrystallization of quartz grains and cement The original sedimentary texture is destroyed, and the rock becomes a mass of interlocking quartz crystals. Where It's Found: - Areas of regional metamorphism - Often in mountain ranges - Areas where sandstone has been deeply buried and metamorphosed Geological Settings: - Core of mountain ranges - Areas of past intense metamorphism - Deep in sedimentary sequences

Physical Properties

Hardness: 7 on Mohs scale (very hard, can scratch glass easily) Durability: Extremely durable and resistant to weathering. One of the hardest common rocks. Fracture: Conchoidal (like quartz) Uses: - Building stone (very durable) - Decorative stone - Crushed stone for construction - Abrasives (in some cases)

Varieties and Types

White Quartzite: Pure quartz, white or light gray. Pink Quartzite: Contains iron oxides, giving pink color. Red Quartzite: Contains hematite, giving red color. Metaquartzite: True metamorphic quartzite (recrystallized). Orthoquartzite: Very well-cemented sandstone that looks like quartzite but hasn't been fully recrystallized.

Rockhounding Value

Collecting Considerations: - Very hard and durable - Sometimes shows interesting textures - Can contain interesting minerals in fractures or layers - Polished specimens are attractive Where to Look: - Mountainous regions - Road cuts - Quarries - Areas with exposed metamorphic rocks What to Collect: - Colorful varieties - Specimens showing crystalline texture - Pieces with interesting features - Polished specimens