Banded Slate or Siltstone with Quartz/Calcite Veins
Protolith-derived Siltstone or Slate (varies based on degree of metamorphism)
Rock Type: metamorphic
Physical Properties
Hardness: 3-5.5 (Mohs scale), Color: Dark grey, charcoal, and light grey bands with white mineral veins. Luster: Dull to earthy (matrix), Vitreous (veins). Structure: Foliated or bedded; fine-grained.
Formation & Geological History
Formed through the compression and low-grade metamorphism of fine-grained sedimentary mud or silt. The white veins are 'secondary mineralization' where hydrothermal fluids filled fractures in the rock long after its initial formation.
Uses & Applications
Common specimens are used primarily for decorative gravel, landscaping, or as educational samples. Highly polished pieces are sometimes used in aquarium decor or pocket stones.
Geological Facts
The distinctive 'racing stripe' on the right rock is a fracture filled with quartz or calcite; this happens when the rock breaks under tectonic pressure and mineral-rich water seeps in to heal the crack.
Field Identification & Locations
Identify in the field by looking for distinct layers (laminae) and cross-cutting white veins that do not match the surrounding matrix. Commonly found in riverbeds, glacial tills, and mountain ranges with sedimentary history.
Identified on: 4/29/2026
Mode: Standard