Concept
Rock (geology)
Overview
In geology, a rock (also called a stone) is any naturally occurring solid mass or aggregate of minerals or mineraloid matter. It is categorized by the minerals included, its chemical composition, and the way in which it is formed. Rocks form the Earth's outer solid layer, the crust, and most of its interior, except for the liquid outer core and pockets of magma in the asthenosphere. The study of rocks involves multiple subdisciplines of geology, including petrology and mineralogy. It may be limited to rocks found on Earth, or it may include planetary geology that studies the rocks of other celestial objects.
Rocks are usually grouped into three main groups: igneous rocks, sedimentary rocks and metamorphic rocks. Igneous rocks are formed when magma cools in the Earth's crust, or lava cools on the ground surface or the seabed. Sedimentary rocks are formed by diagenesis and lithification of sediments, which in turn are formed by the weathering, transport, and deposition of existing rocks. Metamorphic rocks are formed when existing rocks are subjected to such high pressures and temperatures that they are transformed without significant melting.
Humanity has made use of rocks since the time the earliest humans lived. This early period, called the Stone Age, saw the development of many stone tools. Stone was then used as a major component in the construction of buildings and early infrastructure. Mining developed to extract rocks from the Earth and obtain the minerals within them, including metals. Modern technology has allowed the development of new human-made rocks and rock-like substances, such as concrete.
Overview adapted from Wikipedia (CC BY-SA 4.0; see the article history for authors).
In the original texts
Passages from public-domain books where Rock (geology) is discussed.
The prevailing rock is gneiss, often passing, by the disappearance of the quartz and mica, and by the feldspar losing its red colour, into a brilliantly grey primitive greenstone. Not unfrequently quartz and hornblende are arranged in layers in almost amorphous feldspar.
Charles Darwin, Geological Observations on South America
a chapter is titled for it; states what it is; names the idea; opens on it
This variety passes into others of paler green tints, less hard, but with a more crystalline fracture, and translucent on their edges; and these are fusible into a green enamel. Several other varieties are chiefly characterised by containing innumerable threads of dark-green serpentine, and by having calcareous matter in their interstices. These rocks have an obscure, concretionary structure, and are full of…
Charles Darwin, Volcanic Islands
names the idea; a chapter is titled for it; opens on it
for the properties contained in the quarry should be found again in those things which are formed and hewn out of it.” It is in the latter sense that the Almighty is called “rock,” He being the origin and the causa efficiens of all things besides Himself. Thus we read, “He is the Rock, His work is perfect” (Deut. xxxii. 4); “Of the Rock that begat thee thou art unmindful” (Deut. xxxii. 18); “Their Rock had sold…
Moses Maimonides, The guide for the perplexed
names the idea; states what it is; opens on it
The limestone of the Alps, which I have as yet travelled over, has a greyish tint, and beautiful, singular, irregular forms, although the rock is divisible into blocks and strata. But as irregular strata occur, and the rock in general does not crumble equally under the influence of the weather, the sides and the peaks have a singular appearance. This kind of rock comes up the Brenner to a great height. In the region…
Johann Wolfgang von Goethe, Letters from Switzerland and Travels in Italy
names the idea; states what it is; opens on it
As there is but a small distance between the cavern and the surface of the water, it follows, that the water has sunk but very little since the time of the Romans. If it has sunk in the same proportion since the time, when it covered the top of the rock, there is no doubt, but that the time, when it was intirely covered by the sea, must have been very distant. If the same manner of reasoning be used, with respect to…
Various, Philosophical transactions, Vol. L. Part I. For the year 1757.
names the idea; states what it is; opens on it
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