Siltstone (River Rock/Pebble)
Siltstone (Sedimentary Rock) · Decorative Stone / Mineral Specimen
Crystal System
Non-crystalline (Microcrystalline aggregate) / Massive habit
Mineral Group
Silicates (Detrital Sedimentary Rock)
Chemical Formula
Predominantly SiO2 with Al2O3, Fe2O3, and K2O
Formation Process
Sedimentary: Accumulation and lithification of silt-sized particles (0.0039 to 0.0625 mm) under low to moderate pressure.
About This Crystal
The specimen is an opaque, earthy, dark brownish-gray rock. It features a dull/matte luster and a rounded, water-worn shape indicating transport in water. Surface texture is fine-grained and smooth to the touch.
Physical Characteristics
Color: Earthy brown to gray; Streak: White or light brown; Cleavage: None (exhibits bedding planes instead); Fracture: Sub-conchoidal to irregular; Specific Gravity: 2.6-2.7; Fluorescence: Non-fluorescent.
Optical Properties
Opaque; Non-refractive in bulk; No pleochroism or dispersion; Lacks optical phenomena due to fine-grained aggregates.
Hardness & Durability
Origin Region
Globally ubiquitous; typically sourced from riverbeds, floodplains, and sedimentary basins.
Hardness & Durability
Mohs Hardness: 6-7 (depending on quartz content); Toughness: High; Wearability: Good for tumbled stones, though porous.
Care & Maintenance
Wash with warm soapy water and a soft brush. Avoid acidic cleaners which may react with carbonate cements. Generally light-stable.
Rarity & Value
Common; Very low monetary value. Valued primarily as landscaping material or for basic geological study.
Special Characteristics
Features smooth, wind or water-abraded surfaces (ventifact-like appearance) and fine sedimentary layering (laminae).
Lore & History
Historically used for early stone tools and building materials. In lithotherapy, river rocks are traditionally associated with grounding, stability, and the 'flow' of life's transitions.