Crossword-Solution: GROUNDMASS 10 letters, 2 clues 🏆 scrabble score: 14

Some basalts are in large measure glassy (tachylites), and many are very fine grained and compact; but it is more usual for them to exhibit porphyritic structure, showing larger crystals of olivine, augite or felspar in a finely crystalline groundmass.

The inclosures in the larger plagioclastic felspars consist for the most part either of brownish glass, containing fine dark granular matter--probably magnetite, which often renders them opaque,--or of matter similar to that which constitutes the groundmass of the surrounding rock.

The upper half of the drawing is occupied by a crystal of plagioclastic felspar showing twin lamellation and faint zonal markings, and with numerous irregular dark-brown inclosures of glass, probably containing magnetite dust and matter similar to that of the groundmass of the rock which consists of felspar microliths, granules of olivine, and augite crystals, grains of magnetite, and apparently a little interstitial glass.

And within each major classification there may be flows, characterized by banded structures and fine textures; small intrusives composed of well formed crystals in a fine-grained groundmass; and large intrusives consisting of goodsized, equi-granular crystals.

Melilite occurs in the groundmass in large and well-shaped crystals, its dimensions never becoming as small as those of many of the augite crystals.