Paleomagnetic dating definition

24 Feb

Rocks are commonly divided into three major classes according to the processes that resulted in their formation.

These classes are (1) igneous rocks, which have solidified from molten material called magma; (2) sedimentary rocks, those consisting of fragments derived from preexisting rocks or of materials precipitated from solutions; and (3) metamorphic rocks, which have been derived from either igneous or sedimentary rocks under conditions that caused changes in mineralogical composition, texture, and internal structure.

This void space consists of pore space between grains or crystals, in addition to crack space.

In sedimentary rocks, the amount of pore space depends on the degree of compaction of the sediment (with compaction generally increasing with depth of burial), on the packing arrangement and shape of grains, on the amount of cementation, and on the degree of ).

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Likewise, breccia, which contains pieces of other rocks that have been cemented together, and porphyry, which contains interlocking mineral crystals, tend to be rough.

Depending on the type of close-packing of the grains, porosity can be substantial.

It should be noted that in engineering usage— Total porosity encompasses all the void space, including those pores that are interconnected to the surface of the sample as well as those that are sealed off by natural cement or other obstructions.

In a rock these general properties are determined by averaging the relative properties and sometimes orientations of the various grains or crystals. For example, sandstone (characteristically quartzose) has a typical dry bulk density of 2.0–2.6 g/cm also lists representative values for density of seawater, oil, and methane gas at a subsurface condition—pressure of 200 bars (one bar = 0.987 atmosphere, or 29.53 inches of mercury) and a temperature of about 80° C (176° F).) refers to hydrostatic compression.

As a result, some properties that are anisotropic ( differ with direction) on a submicroscopic or crystalline scale are fairly isotropic for a large bulk volume of the rock. For small stresses, the strain is elastic (recoverable when the stress is removed and linearly proportional to the applied stress).