metamorphic
Metaconglomerate
Protolith: Conglomerate (comprising SiO2, Al2O3, etc.)
Hardness: 6-7 Mohs (variable by clast composition); Color: Mottled grey, white, and brown; Luster: Dull to vitreous; Structure: Foliated or non-foliated with stretched/deformed pebbles (clasts); Cleavage: Fractures through clasts rather than around them.
- Hardness
- 6-7 Mohs (variable by clast composition)
- Color
- Mottled grey, white, and brown
- Luster
- Dull to vitreous
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Physical properties
Hardness: 6-7 Mohs (variable by clast composition); Color: Mottled grey, white, and brown; Luster: Dull to vitreous; Structure: Foliated or non-foliated with stretched/deformed pebbles (clasts); Cleavage: Fractures through clasts rather than around them.
Formation & geological history
Formed through the regional metamorphism of sedimentary conglomerate. Under intense heat and pressure, the original pebbles and matrix recrystalize and often flatten or elongate. They are found in ancient mountain belts and cratons.
Uses & applications
Primarily used as a decorative building stone, for heavy construction aggregate, and as a subject for geological study and education.
Geological facts
In metaconglomerate, the 'cement' and 'pebbles' are fused so strongly that when the rock is broken, the fracture usually cuts directly through the pebbles rather than going around them, unlike its sedimentary parent rock.
Field identification & locations
Identify in the field by looking for 'stretched' or 'cigar-shaped' pebbles within a solid crystalline matrix. Commonly found in Precambrian shields like the Canadian Shield or the Appalachian Mountains.
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