IV.—Allotropic Forms of Silica and their Significance as Constituents of Igneous Rocks

1906 ◽  
Vol 3 (3) ◽  
pp. 118-120
Author(s):  
Cosmo Johns
Keyword(s):  
Rock Mass ◽  
Igneous Rocks ◽  
The Other ◽  
Free Silica

That silica appears as a constituent mineral of igneous rocks in two distinct phases, viz. quartz and tridymite, has been known for some time. The writer is not aware that any explanation has been offered which would indicate the conditions determining the appearance of one or the other in a cooling fused rock-mass. He now proposes to describe certain experiments made with a view to explain why it is that though the free silica generally appears as quartz, yet occasionally, as in certain trachytes, it crystallizes out as tridymite.

Isotopic age determinations on clay minerals from lavas and tuffs of the Derbyshire orefield

1972 ◽  
Vol 109 (6) ◽  
pp. 501-512 ◽  
Author(s):  
P. R. Ineson ◽  
J. G. Mitchell
Keyword(s):  
Clay Minerals ◽  
Hydrothermal Alteration ◽  
Igneous Rocks ◽  
The Other ◽  
Mineral Deposits ◽  
Isotopic Age ◽  
Hydrothermal Mineralization ◽  
Pumice Tuff ◽  
Southern Section ◽  
Age Determinations

SummaryEpisodic hydrothermal mineralization has previously been recognized in the northern section of the Pennine orefield. Igneous rocks from the southern section (the Derbyshire orefield) have yielded isotopic ages, some of which are thought to represent ages of hydrothermal metasomatism (deuteric or subsequent). In order to ascertain whether epicyclic hydrothermal events gave rise to the Derbyshire mineral deposits, samples of highly altered doleritic lava and pumice tuff were collected adjacent to areas of mineralization. Clay-mineral concentrates from 34 samples were dated by the potassium–argon method. The conclusions drawn from these analyses support a hypothesis of repeated hydrothermal alteration of the clay minerals, reflecting at least two episodes of mineralization, one about 270 m.y., the other about 235 m.y. The geo-chronological significance of these and other results is considered.

Ferrodiorite from the Isle of Skye

1962 ◽  
Vol 33 (256) ◽  
pp. 26-36 ◽  
Author(s):  
L. R. Wager ◽  
E. A. Vincent
Keyword(s):  
Igneous Rocks ◽  
The Other ◽  
Hybrid Origin ◽  
Skaergaard Intrusion ◽  
The One ◽  
Isle Of Skye

Summary As a preliminary to an account of the marscoite suite of the Western Redhills Tertiary igneous centre of Skye, a description is given here of one unit, the ferrodiorite. While accepting Harker's hypothesis of the hybrid origin of marscoite (1904, pp. 175–196) we consider that the ferrodiorite, with which marscoite on Marsco is associated, is not itself a hybrid, but one of the parents from which the hybrids were formed. Among Thulean igneous rocks the ferrodiorite has mineralogical and chemical affinities with Hebridean mugearites, on the one hand, and with the ferrogabbros of the Skaergaard intrusion on the other, but is probably significantly different from both.

Seepage Stability Analysis for Surrounding Rock Mass of Diversion Tunnel by FEM

2013 ◽  
Vol 787 ◽  
pp. 622-625
Author(s):  
Yun Feng Xu ◽  
Zhen Zhong Shen ◽  
Chao Xin Shao
Keyword(s):  
Finite Element Method ◽  
Rock Mass ◽  
Working Conditions ◽  
Cross Sections ◽  
Surrounding Rock ◽  
The Other ◽  
Seepage Field ◽  
Diversion Tunnel ◽  
Pressure Method ◽  
Seepage Model

Based on the actual conditions of the project and related experience, the seepage model of diversion tunnel and its surrounding rock mass was built to analyze its seepage stability. The seepage field was calculated by using finite element method (FEM) and cut-off negative pressure method. Two typical cross-sections and working conditions were chosen to evaluate the seepage stability of the surrounding rock mass. According to the results, the seepage gradient is larger when one tunnel is filled with water while the other is empty. The maximum seepage gradient is less than the allowable seepage gradient, so the surrounding rock mass of the diversion tunnel can meet the demand of seepage stability.

VI.—The Petrology of Arran

1913 ◽  
Vol 10 (7) ◽  
pp. 305-309 ◽  
Author(s):  
G. W. Tyrrell
Keyword(s):  
Great Britain ◽  
Igneous Rocks ◽  
The Other ◽  
Red Sandstone ◽  
Neighbouring Area

The Riebeckite-Orthophyre of the Holy Isle.—Four Occuxrences of acid and sub-acid igneous rocks containing the rare soda-amphibole riebeckite have been recognized in Great Britain, of which that of Ailsa Craig is the best known. The occurrences of Ailsa Craig and Mynydd Mawr, Carnarvonshire, are riebeckite-microgranites or paisanites. They contain ragged moss-like areas of riebeckite, together with microphenocrysts of quartz and alkalifelspar, in a microcrystalline groundmass of quartz and felspar. Riebeckite was also found by Dr. Teall in the granophyre of Meall Dearg and the neighbouring area of Druim an Eidhne, Skye. Harker described the riebeckite in these rocks as occurring in two forms, one having the usual ragged, sponge-like appearance, and the other being idiomorphic, the faces in the prism zone being well-defined, but with irregular terminations. The fourth occurrence differs somewhat from the others. This rock occurs as an intrusion into the Upper Old Red Sandstone, or Calciferous Sandstone of Easter Eildon Hill, Melrose, and was described by Barron as riebeckite-trachyte or phonolite. It consists principally of sanidine, occurring both as microphenocrysts and in the groundmass, with interstitial patches of riebeckite, and a little nepheline. Harker describes the rock as an orthophyre.

scholarly journals Rock Types Classification and Distribution on Anabanua Village, Barru Regency, South Sulawesi

2020 ◽  
Vol 8 (1) ◽  
pp. 1-8
Author(s):  
Muhammad Resky Ariansyah ◽  
Muhammad Fawzy Ismullah Massinai ◽  
Muhammad Altin Massinai
Keyword(s):  
Sedimentary Rocks ◽  
Research Area ◽  
Igneous Rocks ◽  
The Other ◽  
Metamorphic Rocks ◽  
Geological Process ◽  
Rock Types ◽  
South Sulawesi ◽  
Geological Conditions ◽  
Limestone Sand

Anabanua Village, Barru Regency is one of the areas in South Sulawesi that has quite unique geological conditions. This condition inseparably comes from the complicated geological process that took place during the formation of the island, Sulawesi. In Anabanua Village, there are many types of rocks such as sedimentary rocks, metamorphic rocks and igneous rocks. This paper aims to map and classify the types of rock by taking samples on different places in the research area. Then we observe the samples physical properties. The results showed, from taking 10 rock samples in different places, they have various characteristics. 8 of them were sedimentary rocks, they are Limestone Quartz, Limestone Sand, Shale, Sandstone, Coal, Limestone Bioturbation, Breccia, and Chert Stone. The other 2 samples were metamorphic rocks, they are Greenschist and Quartzite.

Açıksaray “Open Palace”: a Byzantine rock-cut settlement in Cappadocia

2014 ◽  
Vol 107 (2) ◽  
Author(s):  
Fatma Gül Öztürk
Keyword(s):  
Rock Mass ◽  
Volcanic Rock ◽  
Domestic Architecture ◽  
The Other ◽  
Central Anatolia ◽  
Site Analysis ◽  
Close Proximity ◽  
Survey Results

AbstractCourtyard complexes formed entirely out of the volcanic rock mass in Cappadocia, in Central Anatolia, differ from the other rock-cut structures in the region, in both scale and elaboration of design. There are more than forty such complexes in Cappadocia, either gathered in one location or isolated. Located on the Nevşehir-Gülşehir road, Açıksaray contains nine such complexes in close proximity, many of which feature monumental façades as well as reception areas and utilitarian spaces such as large stables around a courtyard. This paper, in the light of survey results, presents site analysis and architectural readings that lead the discussion of the nature and stages of occupation at Açıksaray. By doing this, the paper aims to bring new insights to the discussion on courtyard complexes, adding details and nuance to our understanding of the Açıksaray settlement, while noting similarities with other settlements in the region. Underlining the secular and elite character of the Açıksaray settlement, this study contributes in particular to enlarging the picture of medieval life in Cappadocia, and in general to the studies of Byzantine domestic architecture, for which architectural evidence is still scarce.

Chlorites in a spectrum of igneous rocks: mineral chemistry and paragenesis

1995 ◽  
Vol 59 (394) ◽  
pp. 129-141 ◽  
Author(s):  
Abdel-Fattah M. Abdel-Rahman
Keyword(s):  
Structural Type ◽  
Mineral Chemistry ◽  
Igneous Rocks ◽  
The Other ◽  
High Alumina ◽  
X Ray Diffraction ◽  
Calc Alkaline ◽  
Peralkaline Granite ◽  
Igneous Complexes ◽  
Data Points

AbstractThe chlorite data presented are from four igneous complexes covering the compositional spectrum of igneous rocks (gabbro to granite) of orogenic and anorogenic settings. The four igneous complexes are; early orogenic gabbro-diorite-tonalite (D-T) suite, late orogenic granodiorite-adamellite (G-A) suite (both are calc-alkaline suites), high-alumina trondhjemite (TR), and anorogenic peralkaline granite (PGR).Chlorites in these igneous rocks show characteristic compositional fields. The Mg vs Fe plot provides the best discriminant, as data points define three compositionally different groups. Phases in the PGR are Fe-rich, siliceous, interlayered chlorite-smectite (Fe/Mg = 8.6), and differ significantly from those in the calc-alkaline D-T and G-A rocks which are Mg-rich chlorites (Fe/Mg = 0.6–0.8). The X-ray diffraction data for the peralkaline granite samples show superlattice reflections at approximately 31 Å (air-dried) and 34 Å (ethylene glycollated), thus suggesting the presence of an expandable (smectite-like) component in this interlayered (chlorite-smectite) phyllosilicate phase. Chlorites in the peraluminous TR rocks contain Fe/Mg values intermediate between the other two types (Fe/Mg = 1.3). Tetrahedral Al (AlZ) values are remarkably low (0–0.5) in phyllosilicates in the PGR, but vary from 1.9–2.5 in chlorites from the other suites. Yet, these chlorite groups with their generally low AlZ values are distinct from the more stable (type IIb) metamorphic chlorites. Sedimentary chlorites are somewhat similar, in their low AlZ values and metastable structural type, to chlorites in igneous rocks.In the calc-alkaline rocks, chlorite may have been formed at the expense of both biotite [biotite + 3M + 3H2O = chlorite + A], and calcic amphibole [2 Ca-amphibole + 6H2O + 5O2 + 1.8Al = 1 chlorite + 8SiO2 + A], where M = Fe, Mg, Al, and A = K, Na, Ca. The alteration of alkali amphibole in the peralkaline rocks may have produced interlayered chlorite-smectite via this reaction; [1 Na-amphibole + 7H2O + 2.5O2 + M = 1 chlorite-smectite + A]. The presence of such interlayered chlorite-smectite which typically form at low T (150–200°C) suggests that the region was not affected by any major reheating events, which is consistent with the nature of the feldspars.

scholarly journals Construction of Pressure Tunnels

2019 ◽  
Vol 66 (3-4) ◽  
pp. 77-100
Author(s):  
Lesław Zabuski
Keyword(s):  
Rock Mass ◽  
Numerical Analysis ◽  
Finite Difference Method ◽  
Water Reservoir ◽  
The Other ◽  
Clay Shales ◽  
Carpathian Flysch ◽  
Internal Forces ◽  
The Finite Difference Method ◽  
Preliminary Support

AbstractThe paper focuses on two pressure tunnels in the design of “Kąty-Myscowa” water reservoir. One of them serves as a discharge conduit, whereas the other plays an energetic role. Their depths range between 0 and 75 metres and their diameters equal 5 m. Tunnels are located in the rock mass of Carpathian flysch which is anisotropic and heterogeneous, composed of layers of sandstone and clay shales and intersected with interbedding fissures and numerous joints. The paper is divided in two parts. The first part focuses on methods of excavating and supporting, as well as injecting and sealing (i.e. waterproofing) the tunnel. In the second part, a numerical analysis using the FLAC2D code based on the finite difference method was carried for calculating displacements and internal forces in the preliminary support and in permanent lining. Results of the analysis allow for the assessment of conditions in the tunnel during its excavation and exploitation stages.

scholarly journals III.—On Some Quartz-schists from the Alps

1893 ◽  
Vol 10 (5) ◽  
pp. 204-210
Author(s):  
T. G. Bonney
Keyword(s):  
Igneous Rocks ◽  
The Other ◽  
Metamorphic Rocks ◽  
The Alps

A thick mass of bedded schists, as I have described in more than one paper, occupies the highest position among the socalled metamorphic rocks of the Alps. With the exception of some gneisses—so far as I know of a porphyritic character, and almost certainly intrusive granites modified by pressure— and various green schists, which, in part at least, are basic igneous rocks, similarly affected, the group, which may be traced from one end of the chain to the other, consists of altered sediments.

III.—On the Classification and Nomenclature of Rocks

1875 ◽  
Vol 2 (12) ◽  
pp. 583-587
Author(s):  
S. Allport
Keyword(s):  
Igneous Rocks ◽  
The Other ◽  
Granitic Rocks ◽  
Acidic Group

In the September Number of the Geol. Mag. pp. 425, 426, there are some remarks by Mr. G. H. Kinahan on the nomenclature of certain igneous rocks, on which I should like to offer a few observations. The rocks referred to belong to the acidic group, and are mentioned under the various names of granite, nevadite, granitic rhyolite, liparite, trachyte, elvanite, siliceous elvanite, felstone, bottleite, trachalite; the two last being synonymous, for it appears that bottleite is the local name for a vitrioid rock pronounced to be trachalite; but several of the other names are also synonymous or useless, for we are told that nevadite—a proposed new addition to our granitic rocks—is characterized by a more or less crystalline felsitic matrix inclosing crystals of quartz, one or two felspars with mica or amphibole.

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