Quartzite

Hardness: 7 on Mohs scale. Color: Often white or light-colored, but can be gray, pink, purple, or red due to impurities. Luster: Vitreous to greasy. Crystal structure: Typically massive, granular interlocking crystals. Cleavage: None, fractures conchoidally or irregularly. Specific Gravity: 2.65-2.70.

Formed from sandstone that has been metamorphosed through heat and pressure, typically during regional metamorphism associated with mountain building. The original quartz grains recrystallize, forming a mosaic of interlocking crystals that are much stronger than the original sandstone. Geological Age: Varies widely, depending on the age of the original sandstone and the metamorphic event.

Industry: Used as an aggregate in construction (road building, concrete), railroad ballast, and in the manufacturing of refractory bricks due to its high silica content and heat resistance. Construction: Excellent building material for flooring, wall cladding, countertops, and decorative landscaping due to its durability and aesthetic appeal. Art/Jewelry: Less commonly used for fine jewelry, but can be carved into ornamental objects or used as beads when colored varieties are found. Its robust nature makes it suitable for outdoor sculptures.

Quartzite is one of the most durable and weather-resistant rocks. It is chemically stable and resistant to most forms of weathering. The purity of quartzite can exceed 99% pure silica. The recrystallization process during metamorphism makes quartzite exceptionally tough, often breaking across grain boundaries rather than around them, distinguishing it from sandstone.

In the field: Identify by its extreme hardness (scratches steel easily), granular interlocking texture, and typically vitreous luster. It will not effervesce in acid (unless it contains carbonate impurities) and often has a sugary appearance on broken surfaces. Unlike sandstone, quartzite does not feel gritty when rubbed. Common locations: Found in areas that have undergone significant tectonic activity and metamorphism, such as mountain ranges worldwide (e.g., Appalachians in North America, Himalayas in Asia). Tips for collectors: Look for outcrops in historically active geological regions. Freshly broken surfaces reveal its characteristic texture and luster. Note any color variations as these can indicate interesting mineral impurities.