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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.


These ebonite applications are from the 19th century. Credit: FBQ.

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


Limonite is an amorphous mineraloid of a range of hydrated iron oxides. Credit: USGS.

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]


Hand sample including natural asphalt, from Slovakia. Credit: Piotr Gut.

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.


Ozokerite is from the Bringham Young University Department of Geology, Provo, Utah, collection. Credit: Andrew Silver, USGS.

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


These are naturally occurring amber stones. Credit: Lanzi.
This is natural blue dominican amber. Credit: Vassil.

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


This is a specimen of obsidian from Lake County, Oregon. Credit: Locutus Borg.

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.


These are blue opals from Succor Creek, Oregon, USA. Credit: Rica Rika.
This is an idealized diagram of the apparent structure of opal. Credit: Dpulitzer.
Massive dark blue and fluorescent banded opal from Barco River, Queensland, Australia. Credit: Aramgutang.{{free media}}

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.


Various natural pearls are shown. Credit: MASAYUKI KATO.

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.


Ho-Mg-Zn dodecahedral quasicrystal, grown by using the self-flux method (excess Mg), and slowly cooling from 700 C to 480 C. Credit: Ames Laboratory, US Department of Energy.

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.

External links[edit]

  1. "mineraloid". San Francisco, California: Wikimedia Foundation, Inc. April 20, 2011. Retrieved 2012-10-23.
  2. Philip B. Gove, ed. (1963). Webster's Seventh New Collegiate Dictionary. Springfield, Massachusetts: G. & C. Merriam Company. p. 1221. |access-date= requires |url= (help)
  3. MacEachern, Scott (1996) "Iron Age beginnings north of the Mandara Mountains, Cameroon and Nigeria" pp. 489–496 In Pwiti, Gilbert and Soper, Robert (editors) (1996) Aspects of African Archaeology: Proceedings of the Tenth Pan-African Congress University of Zimbabwe Press, Harare, Zimbabwe, ISBN 978-0-908307-55-5; archived here by Internet Archive on 11 March 2012
  4. Diop-Maes, Louise Marie (1996) "La question de l'Âge du fer en Afrique" ("The question of the Iron Age in Africa") Ankh 4/5: pp. 278–303, in French; archived here by Internet Archive on 25 January 2008
  5. Boswell, P. F. and Blanchard, Roland (1929) "Cellular structure in limonite" Economic Geology 24(8): pp. 791–796
  6. Northrop, Stuart A. (1959) "Limonite" Minerals of New Mexico (revised edition) University of New Mexico Press, Albuquerque, New Mexico, pp. 329–333 }}
  7. Constantinou, G. and Govett, G. J. S. (1972) "Genesis of sulphide deposits, ochre and umber of Cyprus" Transactions of the Institution of Mining and Metallurgy" 81: pp. 34–46
  8. asphalt. San Francisco, California: Wikimedia Foundation, Inc. 20 October 2014. Retrieved 2015-01-09.
  9. "amber". San Francisco, California: Wikimedia Foundation, Inc. 19 December 2014. Retrieved 2015-01-09.
  10. tektite. San Francisco, California: Wikimedia Foundation, Inc. August 31, 2012. Retrieved 2012-10-23.
  11. Poccil (20 October 2004). "pearl". San Francisco, California: Wikimedia Foundation, Inc. Retrieved 2015-07-19.