sedimentary
Greywacke with Quartz Vein
Greywacke (immature sandstone) with SiO2 inclusions
Hardness: 6-7 (Mohs scale), Color: Dull grey to greenish-grey with white veins, Luster: Dull/Earthy, Crystal Structure: Microcrystalline matrix with visible quartz veins, Cleavage: None.
Identified More sedimentary →
Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness: 6-7 (Mohs scale), Color: Dull grey to greenish-grey with white veins, Luster: Dull/Earthy, Crystal Structure: Microcrystalline matrix with visible quartz veins, Cleavage: None.
Formation & geological history
Formed by the rapid deposition of poorly sorted sediment in deep marine environments (turbidity currents), often dating back to the Paleozoic or Mesozoic eras. The white veins are later hydrothermal quartz fills.
Uses & applications
Commonly used as crushed stone for road construction, railroad ballast, and aggregate in concrete. Smooth river-worn specimens are used in landscaping.
Geological facts
Greywacke is often referred to as 'dirty sandstone' because of its high clay and rock fragment content. The quartz veins represent fractures where mineral-rich water once flowed.
Field identification & locations
Identify in the field by its dark, gritty appearance and extreme hardness compared to shale; look for white lines of quartz cutting across the grain. Found worldwide in mountain-building zones.
More like this
Other sedimentary specimens
Sandstone or Siltstone
Arenite (if sandstone)
Sedimentary
Sandstone Grain
Clastic Sedimentary Rock Grain (SiO2 dominated)
sedimentary
Sandstone
Arenite (primarily SiO2)
sedimentary
Shale or Slaty Mudstone
Argillaceous sedimentary rock
sedimentary
Chert Breccia
Brecciated Chert (Microcrystalline Silica)
sedimentary
Sandstone
Arenite
sedimentary