noun. (geology) the matrix of fine-grained crystalline material in which larger crystals are embedded.
- igneous rock
- ground (English)
- grund (Old English (ca. 450-1100))
- mass (English)
- masse (Middle English (1100-1500))
Example sentences of the word groundmass
1. Noun, singular or mass
Buff pumice is similar to its formation as light gray; it can occur when a transparent, colorless groundmass is present with few microcrysts.