Mudstone
Sedimentary Mudstone (unclassified silicate mix) · Decorative Stone / Geological Specimen
Crystal System
Amorphous/Microcrystalline; massive habit with no visible crystal faces
Mineral Group
Silicates (primarily Phyllosilicates/Clay minerals)
Chemical Formula
Variable; primarily SiO2 (silica) with Al2Si2O5(OH)4 (kaolinite) and other clay minerals
Formation Process
Sedimentary; formed by the lithification (compaction and cementation) of silt and clay-sized particles
About This Crystal
Opaque, earth-toned grayish-brown stone with a matte/dull luster and a smooth, water-worn flat tabular shape
Physical Characteristics
Color: Gray-brown; Streak: White to light gray; Cleavage: None (may show fissility); Fracture: Sub-conchoidal to uneven; Specific Gravity: 2.4-2.8; Non-fluorescent
Optical Properties
Opaque; No visible refractive index or birefringence; dull surface reflectance
Hardness & Durability
Origin Region
Globally ubiquitous; found in riverbeds, floodplains, and ancient lake deposits
Hardness & Durability
Mohs hardness: 2.5 - 4; brittle toughness; low durability for jewelry; sensitive to physical scratching
Care & Maintenance
Wash with warm soapy water; avoid abrasive cleaners; store separately to prevent scratching from harder stones
Rarity & Value
Very common; low monetary value; typically collected for educational or decorative purposes
Special Characteristics
Absence of visible grains; potential for micro-fossils; earthy odor when damp
Lore & History
Historically used in pottery and early construction; traditionally associated with grounding and stability in lore