Proceedings of the United States National Museum . on-spicuous. Occasionally a largeclear-cut grain is seen, whichmaybe an early crystallization,but usually the mineral occursas small ragged grains grownaround the boundaries of py-roxene or iron ore and more orless associated with a yellowish green fine scaly serpentinous or chlo-ritic alteration product. The biotite may in large part be a late reac-tion product. It is mostly of the usual type with small axial angle,biaxial negative character, and intense pleochroism in Ught and darkred-brown shades, the absorption being, however, unusual in t
Proceedings of the United States National Museum . on-spicuous. Occasionally a largeclear-cut grain is seen, whichmaybe an early crystallization,but usually the mineral occursas small ragged grains grownaround the boundaries of py-roxene or iron ore and more orless associated with a yellowish green fine scaly serpentinous or chlo-ritic alteration product. The biotite may in large part be a late reac-tion product. It is mostly of the usual type with small axial angle,biaxial negative character, and intense pleochroism in Ught and darkred-brown shades, the absorption being, however, unusual in that it isgreatest in the direction perpendicular to the cleavage. Some crys-tals are pleochroic in pale brown to almost colorless parallel to thecleavage and violet-black to greenish black and almost opaque per-pendicular to the cleavage. Minute ragged grains of biotite occurmixed with grains of hornblende and opaque iron ore in alteredpyroxene individuals, the biotite here evidently being a secondaryproduct derived from alteration of the Fta. 1.— Augite from diabase; sectiok on b(OlO) SHOWING TWINNING AND PARTING PARALLEL TO 0(100)AND CLOSE FARTING PARALLEL TO C(OOl), ALSO SHOW-ING EXTINCTION OF 45° PRODUCING SIMULTANEOUSEXTINCTION IN BOTH HALVES OF THE TWIN. ART. 2. PETROLOGY AT GOOSE CREEK—SHANNON. 13 Apatite is a common though not abundant accessory. It seldomoccurs m the earlier plagioclase and never in the pyroxene. Onecrystal of biotite contained small sharp apatite crystals. The char-acteristic position of the apatite is in the interstitial micropegmatitewhere it forms long needle like prisms penetrating both quartz andfeldspar. Quartz is present in smaU amount with orthoclase, forming rarepatches of fresh sharp micropegmatite occupying smaU angular inter-stices between the other minerals. Iron ore, probably titaniferous magnetite, occurs sporadicaUy aslarge irregular skeletal patches devoid of symmetrv. Much of it ap-pears to be a late introduction develo
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