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Mineralati

Rocks

12 results

Basaltdruse im Museum Mensch & Natur, München. Rock

Basalt

Mohs
5–6
Colour
Dark grey to black
Rock

Conglomerate

Colour
Variable
Armstrong Rocks, Ontario province in Canada. Geographical coordinates are 45°55'90" North and 80°52'00" West and its feature type is Shoal.An amazing collection of rock outcrop that has been weathered by ice and time to produce spectacular art pieces on this uninhabited corner of the globe - also a geologists paradise Rock

Gneiss

Colour
Banded light/dark
Photo: 1 O'clock. Photo Credit: Katelyn Cox. 2012 Photo Contest Rock

Granite

Mohs
6–7
Colour
Light coloured with dark speckles
Pierre de l'autosacrifice, détail. Le roi K'inich Janaab' Pakal. Calcaire. Classique récent (600-900 CE). Provenance: Musée du site de Palanque Alberto Ruiz Lhuillier, Palenque, Chiapas, Mexique. Rock

Limestone

Formula
CaCO3 dominant
Mohs
3–4
Colour
White to grey
Marmor mit Amphibolit-Lagen aus Hartenstein, Waldviertel, Österreich – ausgestellt im Mineralogischen Museum Würzburg Rock

Marble

Formula
CaCO3 recrystallised
Mohs
3–4
Colour
White, coloured veining
(crack surface) Obsidian is a glassy-textured, extrusive igneous rock. Obsidian is natural glass - it lacks crystals, and therefore lacks minerals. Obsidian is typically black in color, but most obsidians have a felsic to intermediate chemistry. Felsic igneous rocks are generally light-colored, so a felsic obsidian seems a paradox. Mafic obsidians are scarce, but they are also black and glassy. Obsidian is an uncommon rock, but can be examined at several famous localities in America, such as Obsidian Cliff at the Yellowstone Hotspot (northwestern Wyoming, USA) and Big Obsidian Flow at the Newberry Volcano (central Oregon, USA). Obsidian is moderately hard and has a conchoidal fracture (smooth and curved fracture surface), with sharp broken edges. Freshly-broken obsidian has the sharpest edges of any material known, natural or man-made (as seen under a scanning electron microscope). Obsidian forms two ways: 1) very rapid cooling of lava, which prevents the formation of crystals; 2) cooling of high-viscosity lava, which prevents easy movement of atoms to form crystals. An example of obsidian that formed the first way is along the margins of basaltic lava flows at Kilaeua Volcano (Hawaii Hotspot, central Pacific Ocean). Most obsidian formed the second way. Seen here is silver-sheen obsidian, an unusual variety. The "sheen" effect is from different indices of refraction between two types of glass in the obsidian: the matrix obsidian and small, flow-aligned, gas-filled or glass-filled lenticular vesicles (Ma et al., 2001). The vesicles are probably incorporated and remelted fragments from an older volcanic unit. Locality: unrecorded / undisclosed site attributed to Mexico Reference cited: Ma et al. (2001) - Micro-analytical study of the optical properties of rainbow and sheen obsidians. The Canadian Mineralogist 39: 57-71. Rock

Obsidian

Formula
Mostly SiO2 glass
Mohs
5–5.5
Colour
Black, dark
Rock

Pumice

Colour
Light grey to white
Polycrystalline quartz granule in sandstone. This photomicrograph is one of a pair, one of which was taken in plane polarized light and the other was taken with crossed polars. You can view the other image by clicking on the file history tab for this image. Rock

Sandstone

Colour
Variable
Rock

Schist

Colour
Silvery to varied
Rock

Shale

Colour
Grey to black
Block of red Ordovician slate with bed, 1 inch of Limestone, green and purple slate, diagonal to the cleavage. From near Hatch Hill, Whitehall, Washington County, New York. Photograph by T. Nelson Dale. Plate 2 A, Slate Deposits and Slate Industry of the United States, U. S. Geological Survey Bulletin 275, 1906. Original caption: RED SLATE WITH BED OF LIMESTONE AND GREEN SLATE, Block of reddish slate from quarries 1 1/2 miles south of Hatch Hill, in Whitehall, N. Y., with bed of limestone bordered by green and purple slate, making a "ribbon," an inch in vertical thickness, crossing the cleavage diagonally, Scale on rule is 4 inches long. The rock is likely from Quarry 33 shown in The slate belt of eastern New York and western Vermont by T. N. Dale, published in Nineteenth Annual Report of the United States Geological Survey to the Secretary of the Interior 1897 - 1898: Part III - Economic Geology, Annual Report 19, by: Charles D. Walcott, 1899. Coordinates of the quarry are 43.476341 N, 73.317278 W. It is thus likely to be from the Ordovician Indian River Formation. Rock

Slate

Colour
Grey, green, purple, black