Conglomerate
Sedimentary Conglomerate · Mineral Specimen / Sedimentary Rock
Crystal System
Amorphous/Polycrystalline (Massively clastic with random orientation)
Mineral Group
Sedimentary Lithology (Primarily Silicate-based clasts)
Chemical Formula
SiO2 (dominant as quartz/clasts) with various mineral inclusions
Formation Process
Sedimentary: Formed by the lithification of rounded gravel and boulders (clasts) larger than 2mm, cemented together by a fine-grained matrix of silt, clay, or chemical cement.
About This Crystal
A coarse-grained sedimentary rock composed of rounded clasts embedded in a dark, fine-grained matrix. The clasts are predominantly white and grey quartz, appearing translucent to opaque with a vitreous to earthy luster.
Physical Characteristics
Color: Multi-colored clasts (white, grey, tan) in a dark grey to black matrix. Streak: White (from quartz). Fracture: Irregular/granular. Specific Gravity: 2.6-2.9. Non-fluorescent.
Optical Properties
Opaque as a whole; individual quartz clasts are translucent with simple refractive indices (approx 1.54) but no notable play of color or pleochroism.
Hardness & Durability
Origin Region
Found globally in riverbeds, alluvial fans, and ancient shorelines; common in the Appalachian Mountains and Swiss Alps.
Hardness & Durability
Mohs Hardness: 6.5-7.0 (clasts) and 3.0-5.0 (matrix). Toughness is variable depending on the strength of the cementation; matrix can be brittle.
Care & Maintenance
Clean with warm soapy water and a soft brush. Avoid harsh acids which may dissolve carbonate cements. Store away from harder minerals to prevent scratching the matrix.
Rarity & Value
Very Common. Value is low, primarily as a geological specimen or for decorative landscaping. No common treatments or enhancements.
Special Characteristics
Features 'clastic texture' with rounded pebbles indicating long-distance transport by water before deposition; may contain small jasper or agate inclusions.
Lore & History
Historically used as a building material and road aggregate. In folklore, it is sometimes called 'Puddingstone' and is traditionally associated with grounding and gathering disparate energies together.