Draft:Solids

Among the common states of matter (gas, liquid and solid), the liquid and solid states have higher density. It is often useful to classify the states of matter according to their relative kinetic and potential energy scales (KE vs PE):

Gas: KE >> PE;

Liquid: KE ~ PE;

Solid: KE < PE.

Therefore, the solid state is characterized by very localized constituent units (atoms, molecules or ions). At all temperatures, atoms in a solid vibrates in the vicinity of their equilibrium positions. Another significant difference between the solids and fluid phases (liquid and gas) is that a solid has a non-zero shear modulus; that is, a finite deformation of a solid can only be caused by a finite force.

The solid state materials can be categorized based on the presence/absence and the type of order. In a crystalline material, the crystalline order is characterized by the translational symmetry, which are defined by the unit cell vectors and the sums of their integer multiples. That is, if you start from one point in a crystal, and travel along a vector that is the sum of integer multiples of the unit cell vectors, at the end of your trip, you will be sitting at a point in an environment identical to your starting point. A result of the three-dimensional periodicity is that a crystal shows sharp peaks in the diffraction patterns when irradiated with x-rays, electron or neutrons. In an amorphous material, such translational symmetry is not present, but local order may still be observed because of local bonding. The diffraction patterns of amorphous materials do not have sharp peaks, a signature of the lack of long-range order. In a quasicrystal, three-dimensional translational symmetry is absent. However, the structure of a quasicrystal may be viewed as a projection of periodic structure in higher dimensions, and as a consequence, quasicrystals exhibit sharp diffraction peaks -- hence the name "quasicrystal".

There are other ways to categorize solid state materials. Based the electrical conductivity, there are metals, insulators and superconductors. Based on magnetic properties, a solid can be said to be diamagnetic, paramagnetic, ferromagnetic, ferrimagnetic or antiferromagnetic. Based on the bonding and constituent units, there are covalent, metallic, and molecular solids.

Even though real solids have finite sizes and definite shapes, typically we start understanding the structure and properties of a solid by first looking at the thermodynamic limit, that is, infinite size without a boundary (or often, with a periodic boundary condition). Quantum theory, in conjunction with statistical mechanics, is at the heart of modern understanding of the solid state. It will always keep it's shape.

Def. "[a] substance that resembles a mineral but does not exhibit crystallinity"^[1] is called a mineraloid.

As with minerals and rocks, mineraloids can also be solids.

Def. a "hard rubber especially when black or unfilled"^[2] is called an ebonite.

Limonite is an iron ore consisting of a mixture of hydrated iron(III) oxide-hydroxides in varying composition. The generic formula is frequently written as FeO(OH)·nH₂O, although this is not entirely accurate as the ratio of oxide to hydroxide can vary quite widely. Limonite is one of the two principle iron ores, the other being hematite, and has been mined for the production of iron since at least 2500 BCE.^[3][4]

Although originally defined as a single mineral, limonite is now recognized as a mixture of related hydrated iron oxide minerals, among them goethite, akaganeite, lepidocrocite, and jarosite. Individual minerals in limonite may form crystals, but limonite does not, although specimens may show a fibrous or microcrystalline structure,^[5] and limonite often occurs in concretionary forms or in compact and earthy masses; sometimes mammillary, botryoidal, reniform or stalactitic. Because of its amorphous nature, and occurrence in hydrated areas limonite often presents as a clay or mudstone. However there are limonite pseudomorphs after other minerals such as pyrite.^[6] This means that chemical weathering transforms the crystals of pyrite into limonite by hydrating the molecules, but the external shape of the pyrite crystal remains. Limonite pseudomorphs have also been formed from other iron oxides, hematite and magnetite; from the carbonate siderite and from iron rich silicates such as almandine garnets. Limonite usually forms from the hydration of hematite and magnetite, from the oxidation and hydration of iron rich sulfide minerals, and chemical weathering of other iron rich minerals such as olivine, pyroxene, amphibole, and biotite. It is often the major iron component in lateritic soils. One of the first uses was as a pigment. The yellow form produced yellow ochre for which Cyprus was famous.^[7]

Def. a "sticky, black and highly viscous liquid or semi-solid, composed almost entirely of bitumen, that is present in most crude petroleums and in some natural deposits"^[8] is called an asphalt.

Def. a natural, waxy hydrocarbon mineraloid is called a zietrisikite.

Def. a natural dark, or black, odoriferous mineraloid wax is called ozokerite, or ozocerite.

Def. a "hard, generally yellow to brown translucent fossil resin"^[9] is called an amber.

An example of obsidian is shown on the right. Obsidian is a naturally occurring glass. Glass is an extremely viscous liquid.

Def. a naturally occurring black glass is called an obsidian.

Def. "[a] small, round, dark glassy object, composed of silicates"^[10] is called a tektite.

Def. a naturally occurring, hydrous, amorphous form of silica, where 3% to 21% of the total weight is water is called an opal.

On the right are light blue opals from Succor Creek, Oregon, USA. On the left is an idealized diagram of the structure of opal consisting of spheres of silica arranged in an orderly manner.

On the lower left, by contrast to the light blue opals on the right, is massive dark blue and fluorescent banded opal.

Lechatelierite is amorphous SiO₂, or silica glass.

Def. a "shelly concretion, usually rounded, and having a brilliant luster, with varying tints, found in the mantle, or between the mantle and shell, of certain bivalve mollusks, [...] and sometimes in certain univalves"^[11] is called a pearl.

A crystalline substance that falls into a periodic pattern, or space group, in three dimensions, can be a mineral, or crystalline solid.

A quasicrystal consists of an ordered array of atoms or molecules without periodicity. They display a discrete pattern in X-ray diffraction but do not fall into any space group.

Soil consists of a solid phase of minerals and organic matter (the soil matrix), as well as a porous phase that holds gases (the soil atmosphere) and water (the soil solution).^[12][13][14] Accordingly, soil scientists can envisage soils as a three-state system of solids, liquids, and gases.^[15]

"The carbonate, originally dissolved in the oceans, contains oxygen, whose atoms exist in two naturally-occurring stable isotopes, ¹⁸O and ¹⁶O. The ratio of these two isotopes tells us about past temperatures. When the carbonate solidifies to form a shell, the isotopic ratio in the oxygen (written as δ¹⁸O) varies slightly depending on the temperature of the surrounding water. The change is only a tiny 0.2 parts per million decrease for each degree of temperature increase. Nevertheless, this is sufficient for us to be able to estimate the temperature of the water in which the forams lived millions of years ago. From this, we can see that temperatures in the Arctic Ocean were about 10-15°C warmer at the time of the dinosaurs than they are today!"^[16]

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