All basalt chemical compositions can be plotted in the basalt tetrahedron, which has normative quartz, olivine, nepheline and
augite at the apices.
All are characterized by the presence of lilac to pinkish (probably titanium- bearing)
augite, pointing to alkaline character of the rocks.
Aegirine and aegirine-augite occur as phenocrysts and groundmass in plagioclase phonolite and tephriphonolite;
augite in phonotephrite, monchiquite, and vogesite; and aegirine, aegirine-augite, and salite as acicular bundles to blunt crystals, some wrapping around nepheline or included in analcime, in phonolite (Lindgren and Ransome, 1906; Loughlin and Koschmann, 1935; Thompson et al., 1985; Birmingham, 1987).
3h) is made up of plagioclase, hornblende,
augite, orthopyroxene, quartz, magnetite, titanite, and apatite.
3d).It comprises; plagioclase 50 - 55 Percent , hornblende (hbl), 30 - 40 Percent ,
augite (Aug), 3 - 5 Percent , olivine, 1 - 3 Percent , magnetite, 1 - 2 Percent and apatite in trace amount.
These primary minerals probably included enstatite, forsterite, anorthite,
augite and chromite, but in the immediate vicinity of the nickel mineralization there are little or no remnants of them.
High percentages of igneous plagioclase and
augite in all samples attest to excellent preservation for Late Proterozoic rocks.
Clinopyroxene analyses by SEM-EDS (at Bowdoin College) for mafic samples 114, 158, and 163 (Table 4) show the pyroxene grains to be
augite in composition (Fig.
Mineralogically these rocks comprise of plagioclase, and clinopyroxene (
augite), with minor chlorite and accessory epidote, ilmenite and secondary actinolite.
All gradations exist between samples with relict primary clinopyroxene (
augite), partially pseudomorphed by actinolite, and accompanied by the remainder of the lower grade assemblages described above, to assemblages with actinolite pseudomorphs exhibiting well-developed blue-green hornblende rims with or without relict pyroxene.
He remarked that it was the only locality in the United States at which could be found crystals of "white
augite [diopside] in nearly rectangular prisms." He also noted that "the limestone of Kingsbridge embraces pyroxene, tremolite, mica, fetid quartz, oxide of titanium, adularia, tourmaline and sulphuret of iron." Samuel Robinson, M.D., in his A Catalogue of American Minerals With Their Localities (1825), devoted a full page to Kingsbridge minerals, and in 1842, Lewis Caleb Beck, M.D.
Petrographically, the basalts are described as containing calcic plagioclase,
augite, and rarer pigeonite and bronzite, and Fe-Ti oxides, and vary from holocrystalline to variably vitrophyric ([less than or equal to]30%).
The mineral fragments include quartz, pyroxene,
augite, [nepheline] hornblende, apatite, mica [phlogopite or magnesian biotite], and feldspar.
Where the igneous rock is exposed its texture is very coarse and it is composed of pale gray plagioclase feldspar, greenish black
augite and a small amount of magnetite.
The first specimens found several years ago were sold and traded as
augite crystals, but suspicions about the true nature of the material led to analysis at the SMNH, which showed it to be babingtonite.
