. A treatise on rocks, rock-weathering and soils;. Petrology; Soils. THE THERALITB-BASANITE GEOUP 89 sanidin, hornblende, biotite, hauyne, melanite, perowskite, and a mineral of the spinel group. Chemical Composition. — The following is the composition of (I) a nepheline tephrite from Antao, Pico da Cruz, Azores, and (II) a nepheline basanite from San Antonio, Cape Verde Islands, as given by Eoth.^ Chemical Composition of Tephrite and Basanite Constituents Silica (SiOs) . , . Alumina (AI2OS) . . Iron sesquioxide (FegOs) Iron protoxide (FeO) . Magnesia (MgO) . . Lime (CaO) .... Soda (NasO) ....
. A treatise on rocks, rock-weathering and soils;. Petrology; Soils. THE THERALITB-BASANITE GEOUP 89 sanidin, hornblende, biotite, hauyne, melanite, perowskite, and a mineral of the spinel group. Chemical Composition. — The following is the composition of (I) a nepheline tephrite from Antao, Pico da Cruz, Azores, and (II) a nepheline basanite from San Antonio, Cape Verde Islands, as given by Eoth.^ Chemical Composition of Tephrite and Basanite Constituents Silica (SiOs) . , . Alumina (AI2OS) . . Iron sesquioxide (FegOs) Iron protoxide (FeO) . Magnesia (MgO) . . Lime (CaO) .... Soda (NasO) .... Potash (K2O) .... Water (H2O) ..... II • • •« Structure. — The rocks of this group are as a rule porphyritic with a holoerystalline ground-mass, though sometimes there is present a small amount of amorphous interstitial matter or base; at times amygdaloidal. Colors. — The colors are dark, some shade of gray or brownish. Classification and Nomenclature. — According to their vary- ing mineral composition Eosenbuseh divides them into: Leucite tephrite, Leucite basanite, Nepheline tephrite, Nepheline ba- sanite. The group, it will be observed, stands intermediate between the true basalts and the nephelinites to be noted later. Their distribution, so far as now known, is quite limited. 7. THE PEEIDOTITE-LIMBXTEaiTE GROUP This and the following groups include eruptive rocks in which neither quartz nor feldspars of any kind longer appear as essential constituents. They are therefore very low in silica, and classed as ultrabasic. Although in most cases comparatively insignificant as rock masses, they are peculiarly interesting as *Abliandlungen der Konig. Akad. der Wissenseliaften zu Berlin, 1884, p. 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 wor
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectpetrolo, bookyear1913
