Sandstone (Greywacke/Siltstone)
Sedimentary Rock (Lithic Sandstone/Siltstone) · Decorative Stone / Common Mineral Specimen
Crystal System
Amorphous/Microcrystalline; massive habit with clastic texture. No macroscopic crystal system visible due to sedimentary nature.
Mineral Group
Silicates (primarily Tectosilicates and Phyllosilicates in a sedimentary matrix)
Chemical Formula
Variable; primarily SiO2 (Quartz) with Al2Si2O5(OH)4 (Kaolinite), KAl2(AlSi3O10)(OH)2 (Muscovite), and various lithic fragments.
Formation Process
Sedimentary; formed by the accumulation, compaction, and lithification of sand-sized mineral particles or rock fragments over millions of years.
About This Crystal
Rounded, water-worn pebble with a dull, matte luster. It exhibits an earthy grey to tan color with a granular, fine-grained texture. It is completely opaque with a smooth but porous surface.
Physical Characteristics
Color: Grey/Tan; Streak: White; Cleavage: None (conchoidal to irregular fracture); Specific Gravity: 2.2–2.8 g/cm³; Non-fluorescent under UV light.
Optical Properties
Isotropic; No visible pleochroism, birefringence, or dispersion. Opaque with a matte, non-reflective surface.
Hardness & Durability
Origin Region
Global; common in riverbeds and mountainous regions (e.g., Appalachian Mountains, USA; Scottish Highlands; various river basins).
Hardness & Durability
Mohs Hardness: 6–7 (if quartz-rich); Toughness: Low to moderate; prone to crumbling if poorly cemented. Suitable for decorative garden use but not jewelry.
Care & Maintenance
Wash with warm soapy water and a soft brush. Avoid acidic cleaners which may dissolve carbonate cements. Durable as a tumble-stone but can be scratched by quartz.
Rarity & Value
Common; Minimal monetary value. Primarily valued as landscape material, river rock, or for educational geological collections.
Special Characteristics
Water-rounded shape (alluvial transport); presence of micro-inclusions of clay and mica; potentially shows faint bedding planes under magnification.
Lore & History
Historically used as a building material (brownstone) and for abrasive tools. In traditional lore, it is often associated with grounding, stability, and the element of Earth.