sedimentary or metamorphic
Glacial Erratic (Sandstone/Quartzite)
Glacial Erratic specimen (likely Orthoquartzite or Feldspathic Sandstone)
Hardness: 6-7 (Mohs scale); Color: light grey to tan; Luster: dull to earthy; Crystal structure: granular/clastic; Cleavage: none; Specific Gravity: approx 2.6
- Hardness
- 6-7 (Mohs scale)
- Color
- light grey to tan
- Luster
- dull to earthy
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Physical properties
Hardness: 6-7 (Mohs scale); Color: light grey to tan; Luster: dull to earthy; Crystal structure: granular/clastic; Cleavage: none; Specific Gravity: approx 2.6
Formation & geological history
Transported by glacial ice during the Last Glacial Period (Pleistocene epoch). These rocks are plucked from their parent bedrock and deposited miles away as the ice melts.
Uses & applications
Landscaping, historical/geological study, and occasionally as monumental stone or fill material in construction.
Geological facts
Glacial erratics are 'immigrant' rocks that don't match the local bedrock geology. They provide vital evidence for the direction and extent of ancient ice sheet movements.
Field identification & locations
Identify by its rounded shape (abrasion from ice transport) and its placement on top of different soil or rock types. Look for 'glacial striations' or scratches on its surface.
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