from The Century Dictionary.
- In petrography, noting the structure of some lavas in which microscopic prisms are crowded in a glass matrix.
from Wiktionary, Creative Commons Attribution/Share-Alike License.
- adjective A textural term used in
petrographicclassification of volcanicrocks, referring to a volcanic rock groundmass, which is visible only under magnification with a petrographic microscope, that contains a mixture of very fine-grained mineral crystalseither mixed with natural volcanic glass, or surrounded by thin bands of volcanic glass.
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