igneous
Diorite (likely)
Diorite, an intrusive intermediate plutonic rock
AI-generated identification · may be incorrectCoarse, speckled black-and-white “salt-and-pepper” appearance, likely plagioclase feldspar with dark hornblende and/or biotite. Hardness is roughly 6–7 Mohs; crystals are interlocking, with no prominent cleavage in the rock as a whole. The photograph does not allow confident mineral identification.
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Physical properties
Coarse, speckled black-and-white “salt-and-pepper” appearance, likely plagioclase feldspar with dark hornblende and/or biotite. Hardness is roughly 6–7 Mohs; crystals are interlocking, with no prominent cleavage in the rock as a whole. The photograph does not allow confident mineral identification.
Formation & geological history
Forms when intermediate-composition magma cools slowly underground, allowing visible crystals to grow. Diorite occurs in many ages of continental crust; the specimen’s age cannot be determined from the image.
Uses & applications
Used as crushed aggregate and, when attractive and sound, as dimension or decorative stone; this small rounded specimen is mainly suitable for collecting.
Geological facts
Diorite’s contrasting light and dark minerals create its distinctive speckled pattern; it is sometimes marketed commercially as “black granite.”
Field identification & locations
Look for visible, interlocking light feldspar and dark minerals without the abundant quartz typical of many granites. Found in intrusive bodies worldwide; a fresh surface and mineral tests would help confirm the identification.
