. Bulletin of the Southern California Academy of Sciences. Science; Natural history; Natural history. Bulletin, So. Calif. Academy of Sciences Vol. .57, Part 1. 1958. PLATE 11 Example of orbicular gabbro. Scale is six inches long. Tlie plagioclase averages approximately An 66 in composition and forms more than half of most orbicules. Its wedges and rods, elongated parallel to the a axis, range to one or two cm. in length. The mineral is consistently fresh but carries many inclusions. Whereas hornblende is the predominant dark mineral of the mat]-ix, hypersthene is much the more abundant in the
. Bulletin of the Southern California Academy of Sciences. Science; Natural history; Natural history. Bulletin, So. Calif. Academy of Sciences Vol. .57, Part 1. 1958. PLATE 11 Example of orbicular gabbro. Scale is six inches long. Tlie plagioclase averages approximately An 66 in composition and forms more than half of most orbicules. Its wedges and rods, elongated parallel to the a axis, range to one or two cm. in length. The mineral is consistently fresh but carries many inclusions. Whereas hornblende is the predominant dark mineral of the mat]-ix, hypersthene is much the more abundant in the orbicules, a\eraging 30 percent. It occurs as irregular one-to four-mm. grains elongated roughly parallel to the c axis. These lie be- tween, and moulded against, the plagioclases and occur as gran- ules in the thinner zones. Augite is a much less common pyroxene and occurs as scat- tered anhedral grains rarely exceeding mm. across. Horn- blende, except where it is the principal mineral of a wide zone, is about as common as augite. It has the same pleochroic colors as that in the matrix. Biotite is sometimes present but is the most uncommon ferromagnesian mineral. There are the usual minor accessories such as zircon, apatite and magnetite. 30. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Southern California Academy of Sciences. Los Angeles, Calif. : The Academy
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