11/29/2023 0 Comments Rocks that look like rose quartz![]() The image shows a small pocket with small quartz crystals in an irregular vein in a granitic rock at the Kingston Mountain range in southern California.Ī small piece of the wall of a pocket in a large quartz vein. In other cases there is an obvious pattern in the orientations of the veins: for example, when a igneous rock shrinks during cooling, the cracks may develop into a regular system of fissures that might be filled with quartz from percolating hot brines. Rocks are sometimes cut by quartz veins at random orientations, with or without crystals. From a marble quarry at Josheghan village, at the southern slopes of the Karkas Mountains, Esfahan Province, Iran. It is a polished plate of slightly metamorphosed limestone (that is, it has been turned into marble) with a piece of a fossilized coral reef. This is a very obvious example of a quartz veins that is not related to the initial formation of the rocks it runs through and is caused by tectonic stress. This part of a quartz vein that is outlined with quartz crystals has been found at the foot of the rocks shown in the previous image (Fig.1.3). ![]() Like the veins presented in Figs.1.1 and 1.2, it is made of intergrown, mostly milky crystals. The vein is not massive, but contains small pockets. Crystals were rarely clear at that location and often included small brown stains of iron oxides.Īnother example of vertical quartz veins in a fine-grained volcanic rock of porphyric structure (possibly an andesite) at Monte Santa Miale, north of Seulo, Barbagia, Cagliari Province, Sardegna, Italy. A free standing quartz crystal can be seen sitting in a small pocket in the lower part of the image.Ī small group of quartz crystals that has been worked out of a similar quartz vein at Cala Sarraina beach. ![]() These veins almost always run parallel to the major fracture zones of the large granite batholith that makes up large parts of northern Sardegna and the neighboring island of Corsica.Ī close-up view of one of the veins reveals that these are made of intergrown milky quartz crystals. Vertical quartz veins in a coarse-grained red granite at Cala Sarraina beach, at the northern end of the Costa Paradiso, Trinità d' Agultu, Sassari Province, Sardegna, Italy. Well-formed crystals, if found at all, are only a small portion of the vein filling. In the majority quartz veins, most of the quartz is precipitated as massive, milky quartz. Later, when the crystal growth slows down, the crystals may get less milky or even clear. The result is milky quartz, either massive or made of interlocked milky quartz crystals. Hot brines that enter a crack in the rock from some distant hot source like a granite pluton first cool and precipitate most of their load rather quickly. This process may continue until the crack is completely filled or may stop before, leaving "pockets" in the vein that are sometimes outlined by crystals. Hot brines that percolate the rocks and originate at greater depths with higher temperatures will precipitate the minerals they carry with them in cracks at lower temperatures and pressures. The crack might form during folding of the rock in mountain-building processes, by shattering during tectonic events, by a decrease in pressure during the uplift of a rock, or because a rock cools down and shrinks. The simplest type of a quartz vein is the filling of an already present crack in rocks. The veins can form under various conditions, and depending on these conditions, may or may not contain quartz crystals.Įven though certain types of quartz veins do never bear any crystals, it sometimes makes sense to follow large quartz veins to look for crystal-bearing fissures: Should a rock that contains old large quartz veins have been folded later due to tectonic forces, the quartz veins represented a disturbance (a discontinuity in the otherwise homogeneous mechanical properties), and alpine-type fissures are likely to open up between the quartz and the host rock. Although the term "vein" suggests this, the veins of quartz and other minerals are usually not thin tubes, but rather thin sheets. Quartz is often found in veins that cut through rocks. This section is now a page of its own: Quartz as a Rock-Forming Mineral ![]() ![]() Note that the way the different geological environments have been grouped is to some degree arbitrary and "quartz-centric", so "definitions" of different environments may overlap and environments may possess similar properties. Many of these environments result in a characteristic appearance of the quartz specimen. This chapter presents the most important geological environments in which quartz can be found. ![]()
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