Sample SP21b -Small Dike

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Thin Section from SP21b

Thin-section under crossed-nicols (5 mm in diameter). Notice stellate CPX phenocryst in the center of photo exhibiting hourglass zonation characteristic of Titanaugite.

Thin Section Description

SP21-B (Small Dike). Camptonite. This rock is holocrystalline, porphyritic aphanitic with fine- to medium-grained subhedral to euhedral phenocrysts in a light brown groundmass (20%) of plagioclase and fine-grained mica. All phenocrysts are subhedral except for anhedral grains of olivine (1-3 mm), and opaques (< 1 mm), which are subhedral to anhedral. Anhedral fluorite (<1 mm) is present after iddingsite and possibly hornblende. The following are present as phenocryst phases: sector zoned titanaugite (1-3 mm); biotite (<1 mm), and phlogopite (<1 mm); oscillatory zoned augite (1 mm); plagioclase (1-3 mm) is present with moderate alteration to fine-grained phyllosilicates with some grains exhibiting oscillatory zonation; apatite (<.1 mm). Some of the titanaugite occurs as well- developed stellate clusters (.5-4 mm). The cores of some of the titanaugite grains exhibit a sieve texture. Opaques appear as crystals in the groundmass and as inclusions in biotite and clinopyroxene. The olivine is moderately altered to iddingsite. Amygdules are present with rims of aegerine-augite around feathery-textured fine-grained mica, fine-grained plagioclase, and glass. The overall texture is glomeroporphyritic.