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Glite Dictionary
groundmass

groundmass

9.9
Fine hard rock that holds larger crystals in volcanic rock
  • noun
  • /ˈgraʊndˌmæs/
  • Specialized
: matriz
  • Porphyritic rocks typically show visible crystals embedded in a much finer groundmass.

Examples

  • The large crystals of feldspar were set in a dark basaltic groundmass.

  • Scientists analyzed the groundmass to determine the cooling history of the volcanic rock.

  • The groundmass of the granite was quite uniform.

  • Can you identify the groundmass in this sample?

  • Porphyritic rocks typically show visible crystals embedded in a much finer groundmass.

  • Scientists analyzed the groundmass to determine the cooling history of the volcanic rock.

  • The large crystals of feldspar were set in a dark basaltic groundmass.

Surface Forms

groundmass singular
groundmasses plural

Morphology

groundmass = ground + mass (semi-transparent) = ground + mass

The components 'ground' + 'mass' are recognizable, but the specific technical geological meaning (fine-grained matrix in igneous rocks) is specialized and not directly obvious to general learners.

Etymology

Groundmass is made of two common words, ground ('base' or 'earth') and mass ('bulk' or 'large amount'), so it names the bulk material that forms the base of a rock. That's why in geology groundmass means the fine, small-crystal material that holds larger crystals inside it.