Numerous Pegmatite Research Articles

Homogenous deformation in precambrian supracrustal rocks of Kumlinge area, southwest Finland

Supracrustal rocks form a trough-like prolonged syncline surrounded by granitic rocks. They consist of quartz-feldspar schists (leptites) overlain by amphibolites. The stratigraphic succession in the syncline is as follows: undermost lie leptites followed by amphibolitic pillow lavas, which are gradually superseded by pillow breccias and agglomerates. A small area of polygonally jointed amphibolites lies above the pillow breccias. The succession gives the impression of volcanic activity in a gradually declining depth of water. The pillow lavas and agglomerates are commonly flattened or elongated and only locally undeformed. Elongation-type deformation is most pronounced in the agglomerates of the central parts of the syncline, where it now reaches its maximum breadth. The axial ratios of the elongated agglomerate fragments are approx. 2/3/75. Around the margins of the syncline the pillow lavas are strongly flattened. The most flattened pillows have axial ratios of approx 1/60/60. The flattening deformation in the adjacent leptitic rocks can be estimated from boudinage and folding in numerous pegmatite dikes. The estimated deformation in the leptites agrees reasonably well with the observed deformation in the adjacent pillow lavas. A gravitative sinking of the dense amphibolites into the underlying granitic material could possibly account for variations in the type of deformation within the syncline.

Origin of the nelsonite dikes of Amherst County, Virginia

Numerous bodies of nelsonite have been found in Amherst County, in the Piedmont Province of Virginia. As these bodies consist largely of ilmenite and apatite they are of more than usual economic and scientific interest. Most of them occur as dikes intruded parallel to the foliation of hydrothermally altered Lovingston quartz-mica gneiss, but some also occur in anorthosite. The dikes are believed to be genetically related to somewhat younger hypersthene granodiorite that has invaded the gneiss, and through differentiation also has yielded the anorthosite as well as numerous pegmatites. Intrusion of the granodiorite was followed by hydrothermal solutions that altered the top of the solidified intrusive, the overlying Lovingston gneiss, and the somewhat earlier intruded nelsonite.

Societies and Academies

EDINBURGHRoyal Society, November 5. L. M. DAVIES: The geology of Inchkeith. This island was last surveyed geologically by Sir Archibald Geikie in 1860. Col. Davies replaces Geikie's map by more modern ones; distinguishes between intrusive and extrusive igneous rocks, giving particulars as to their natures; and describes the sedimentary sequence throughout. The drift geology of the island is also systematically described for the first time; and a list is given of the fossils found on Inchkeith. Appendixes are added, on the drift deposits by Dr. R. Campbell, and on the entomostraca by Miss M. H.Latham. C.F.DAVIDSON: The Tertiary geology of the Island of Raasay, Inner Hebrides. The Tertiary igneous rocks of Raasay and South Rona include olivine-basalt lavas, an intrusive suite of acid and basic sills, and a large number of dykes. The major sills are riebeckite-bearing granophyres, and highly differentiated olivine-dolerite (crinanite) types with abundant segregations, including picrite, teschenite, syenite and numerous pegmatites. The petrogenesis of these is discussed. Comparable rocks are found in the dyke-suites, where differentiates also include analcite-basanite and analcite-tephrite. One olivine-dolerite dyke fuses granophyre xenoliths into pitchstone. Other analysed intrusions include a leidleite pitchstone dyke, a peridotite dyke and an elongated boss of gabbroidal teschenite, while a series of vents are believed to represent hot springs of Tertiary age. The paper concludes with notes on the recent earth-movements of these islands. B. P. WIESNER and N. M. SHEARD: The duration of life in an albino rat population. H. W. TURNBULL: The invariant theory of the correlation. This is an extension of methods already utilised in dealing with bilinear and quadratic forms to a class of transformations which occur in algebraic geometry, called correlations. The main results prove to be simpler than might be expected.

Tourmaline and tourmaline schists from Belcher hill, Colorado

Research Article| January 01, 1899 Tourmaline and tourmaline schists from Belcher hill, Colorado Horace B. Patton Horace B. Patton Search for other works by this author on: GSW Google Scholar GSA Bulletin (1899) 10 (1): 21–26. https://doi.org/10.1130/GSAB-10-21 Article history first online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Twitter LinkedIn Tools Icon Tools Get Permissions Search Site Citation Horace B. Patton; Tourmaline and tourmaline schists from Belcher hill, Colorado. GSA Bulletin 1899;; 10 (1): 21–26. doi: https://doi.org/10.1130/GSAB-10-21 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu nav search search input Search input auto suggest search filter All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract IntroductionTourmaline is a not uncommon mineral in the northern part of Jefferson county, Colorado. It is to be found as an ingredient of the quartz-feldspar boulders which strew the mesas bordering the foothills west of Denver and in the beds of the streams which drain the crystalline schists of these foothills. It may also be found in place in the numerous pegmatite veins that everywhere cut the schists. Beautiful lustrous black crystals, often two or more inches in diameter, have been obtained from these pegmatite veins. In rare cases colors other than black may be seen, as for instance, some small crystals, about a quarter of an inch in diameter, with white centers and black margins, found in a pegmatite boulder near Golden.While the pegmatite veins may well be considered the habitat of the Jefferson County tourmalines, in some cases this mineral occurs with somewhat different association. On . . . This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not currently have access to this article.