Tourmaline Grains Research Articles

Surface Microtextures of Heavy Minerals from the Mediterranean Coast of Israel

ABSTRACT Results are reported of SEM examination of grains of magnetite, tourmaline, hornblende, zircon, calcite and quartz from the Mediterranean coast between Tel-Aviv and Acre, including the littoral (swash) zone (in which the sediments are in permanent contact with the sea water), beach sands 7-10 m from the water line (in which contact is occasional), and dunes. The surface microtextures are the result of mechanical and chemical processes (the former shown by comminution studies to modify the grain surfaces in ways that render them more susceptible to chemical attack), and influenced by the physical and chemical properties of the minerals and by the energy and chemistry of the environment. In the swash zone and beach sands, the marks of mechanical and chemical action depend on the crystal structure of the mineral and its resulting cleavage (or parting). In the dunes, this dependence is obviated and a rolling topography (as defined by Krinsley and Doornkamp, 1973) tends to develop, especially in less stable minerals which could thus be used for differentiation of beach and dune sand. The rolling topography or quartz grains from calcareous sandstones of the Late Quaternary, believed to be ancient dunes, exhibits changes due to chemical attack on the calcareous cement. The chemically modified microtextures correlate well with published stability series (Pettijohn, 1957)--the one exception being calcite, which shows crystal growth in the swash zone.

Quaternary sediments at Sungei Besi, West Malaysia

Well stratifi ed sediments consisting of gravel, sand , mud, clay a nd peat crop o ut in several opencast pits of the Sungei Bes i Tin Mines near Kuala Lumpur. They li e unconformably over limestone a nd granite bed rock with their base below the present sea level. Pollen analyses a nd carbon-14 dating ind icate that most of the sed iments are Pleistocene in age. Abundant plant fragments, the lack of marine fossi ls, and the occur­ rence of gravell y lenses suggest a fluvia l depositional environment . The dominance of a ngul a r grains of quartz, tourmaline and muscovite in these sediments indicate that they were derived fro m weathered granitic rocks nearby. The depositi onal hi story was prob­ a bl y related to the sea level changes during the Pleistocene.

Authigenic tourmalines from the lower Kaladgi sandstones, Jamkhandi, Mysore state

ABSTRACT The presence of different varieties of tourmaline with authigenic growths has been observed in the lower Kaladgi sandstones of Jamkhandi. Their details, origin, and significance have been discussed. The authigenesis is due to the development of minerals of complex isomorphous series of tourmaline group on any of the detrital tourmaline grains, irrespective of chemical composition. Based on the physical characters of the detrital tourmalines, the nature of the provenance has been suggested.

HEAVY MINERALS OF THE U. S. SOUTH ATLANTIC CONTINENTAL SHELF AND SLOPE

Heavy minerals from the U. S. South Atlantic continental shelf and upper slope have been studied. In comparison with other areas such as the Gulf of Mexico shelf, both qualitative and quantitative variation in heavy minerals is subdued mainly due to similar provenance areas for most of the major rivers. Two heavy-mineral provinces can be defined, based primarily on the epidote content. A close areal relationship between capes and certain heavy-mineral anomalies was noted indicating that processes forming the capes and their associated seaward-extending shoals are important factors in sediment distribution. Roundness observations were made on garnet, kyanite, staurolite, and tourmaline grains. Garnet and kyanite exhibit strong roundness anomalies, both minerals being better rounded in the northern portions of the study area. Roundness-distribution histograms indicate dual-sediment sources in some instances.

Petrography of the Teays-Mahomet Valley Deposits

ABSTRACT Samples of sediments from just above the bedrock of the valley bottom of the ancient Teays and Mahomet Rivers were taken in unglaciated regions of West Virginia and Ohio, and from beneath glacial drift in Ohio and Illinois and analyzed for heavy mineral content. Analysis of the West Virginia samples showed a mature suite of minerals characterized by rounded grains of tourmaline and zircon, some epidote, a high muscovite content, and the absence of pyroxenes. The Ohio samples contained abundant angular grains of hornblende, a few pyroxene grains, as well as much angular zircon and tourmaline. Analysis of the Illinois samples showed an abundant garnet content with much hornblende, epidote, a small amount of pyroxene, and in general displayed mineralogy typical of the Pleistocene tills. he mature mineralogy of the sediments in the unglaciated area of West Virginia indicates derivation of these sediments from the Paleozoics of the folded Appalachians rather than from the Piedmont. Mineralogy of the sediments in the valley bottom beneath the glacial drift suggests that the Teays-Mahomet alluvium has been scoured from these locations and has been replaced by glacial drift.

Authigenic tourmaline in the Banganapally stage (Kurnool system), India

Records the occurrence of authigenic overgrowths on tourmaline grains (predominantly Fe-schorlite) in orthoquartzite pebbles from the Banganapally conglomerate in the Kalava region.

Size distribution of zircon and tourmaline grains in some samples of the Lissie Formation [Texas

ABSTRACT Zircon and tourmaline grains in samples of the Lissie Formation near Houston, Texas, appear to be log-normally distributed by number percentage. Size distributions of bulk samples (predominantly quartz) are log-normal by weight percentage. The similarity of the distributions may be caused by hydraulic properties of the transporting agent. The size distribution of the heavy minerals may, however, be related solely to distributions in primary source rocks, and the distribution of the light minerals may be controlled entirely by fracturing during the sedimentation process.

V.—Pleochroism in a Tin-bearing Mineral from Siam

In 1915 a heavy concentrate of sand from an unknown locality in Siam was submitted to me for identification. The sand consisted of rather coarse grains of a dark mineral, and finer grains of ilmenite, monazite, tourmaline, zircon, and topaz, with some of the same dark mineral as that occurring in coarse grains.

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