United States or Rwanda ? Vote for the TOP Country of the Week !
The earliest eruptions of lava in the North-east of Ireland belonged to the highly acid varieties, consisting of quartz-trachyte with tridymite. This rock rises to the surface at Tardree and Brown Dod hills and Templepatrick. It consists of a light-greyish felsitic paste enclosing grains of smoke-quartz, crystals of sanidine, plagioclase and biotite, with a little magnetite and apatite.
Under the microscope it is a confused mass of finely granulated minerals, with numerous included crystals. The rock has undergone complete metamorphism and its origin is unknown. 8 Phyllite-Near Otter Lake. A soft extremely fine grained gray rock, with a well developed schistose structure, carrying much magnetite, plagioclase, orthoclase and their alteration products.
The quartz grains show secondary growth. 13 Altered Gabbro Thirty-two Miles Above Wuchusk Nipi on Nascaupee River. A coarse dark green rock whose principal constituents are pyroxene plagioclase and magnetite. There is a slightly developed diabasic structure and the rock is much altered by weathering; the resultant product being chlorite. 14 Quartizite Bibiquagin Lake.
A dark, compact rock, having a mottled appearance due to grains of plagioclase, and a green color in section. Minerals present are hornblende, biotite, plagioclase, pyroxene, quartz and the alteration products from the feldspar. The rock has been subjected to a strong crushing action, which has been resisted by only small portions of it.
The severe crushing to which the rock has been subjected has resulted in the conversion of the plagioclase into scapolite and also in the formation of zoisite by the characteristic alteration of the lime bearing silicate of the feldspar in conjunction with other constituents of the rock. The light mineral is finely granulated and the whole is marked by uneven extinction.
Plagioclase, microcline and quartz are the predominating minerals, while biotite, titanite, epidote, apatite, zircon and garnet are present in smaller quantities. There is also a small amount of hematite, pyroxene and sericite. The rock, which is of a granitic composition, contains numerous crystallites and has been subjected to considerable strain and crushing, which has resulted in foliation.
The rock has probably been derived by dynamic metamorphism, from a coarse igneous rock like a gabbro. 7 Epidotic Sericitic Schist. Washkagama Lake. A fine grained compact gray rock, of aggregate structure, consisting chiefly of quartz, plagioclase and biotite, and the alteration products epidote and sericite.
5-Mica Granite Gneiss Country Rock near Caribou Ridge. In the hand specimen the rock has the same appearance as No. 4, if anything, it is somewhat more compact. The principal minerals are, plagioclase, biotite and microcline, with smaller quantities of quartz, iron oxide, pyroxene and garnet. The feldspar is decomposed with the resulting formation of epidote, which is quite prominent.
Word Of The Day