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Common Classes Of Crystalline Solids, Internal Structures Of Metallic Crystals, Common Internal Structures Of Crystals Of Ionic Solids

A crystal is a solid in which the particles that make up the solid take up a highly ordered, definite, geometric arrangement that is repeated in all directions within the crystal.

Crystals have always attracted the curiosity of humans. Archaeologists have unearthed shells, claws, teeth, and other crystalline solids dating to 25,000 B.C. that have holes, as though worn as necklaces, and that are engraved with symbols of magic. The treasures of the ancient Egyptian king, Tutankhamen, abound with crystals in the forms of gems and jewels. These were not only intended for personal adornment, but were designed in symbolic fashion and believed to possess mystical and religious powers. Healers used crystals in their magical rites and cures.

In ancient Greece, Archimedes made a study of regular solids, and Plato and Aristotle speculated on the relationship between regular solids and the elements. In the sixteenth century, the German naturalist, Giorgius Agricola, classified solids by their external forms, and Johannes Kepler observed that snowflakes were always six-sided (circa 1611), commenting on geometrical shapes and arrangements that might produce this effect. In the seventeenth century, noted philosophers and mathematicians, including René Descartes, Robert Hooke, and Christiaan Huygens followed and expanded Kepler's postulates.

In 1671, an English translation of a study by a Danish-born scientist, Nicolaus Steno, was published in London. It described his investigative work on crystals of quartz, which consists of silicon andoxygen. An Italian scientist, Domenico Guglielmini, developed a structural theory of crystals over the years 1688-1705. Later, measurements of crystals by the French scientist, Jean Baptiste Louis Romé Delisle, were published between 1772-1783. In 1809, the British scientist, William Hyde Wollaston, described an improved goniometer instrument for making accurate measurements on small crystals.

The study of crystals has led to major advances in our understanding of the chemistry of biological processes. In 1867, Louis Pasteur discovered two types of tartaric acid crystals which were related as the left hand is to the right; that is, one was the mirror image of the other. This led to the discovery that most biomolecules, molecules upon which living systems are based, exhibit this same type of "handedness." In fact, scientists have speculated on the possibility of life having evolved from crystals.

Detailed analyses of crystal structures are carried out by x-ray diffraction. In 1912, Max von Laue predicted that the spacing of crystal layers is small enough to cause diffraction (breaking of light, when it hits an opaque surface, into colored bands). William Henry Bragg and his son, William Lawrence Bragg, were awarded the Nobel Prize in chemistry (1915) for their development of crystal structure analysis using x-ray diffraction. In 1953, James Watson and Francis Crick deduced the double helix structure of DNA ( deoxyribonucleic acid, one of the nucleic acids which controls heredity in living organisms) partly from the results of x-ray diffraction analysis of DNA. In recognition of this advancement in the study of the processes of life, they were awarded the Nobel Prize in 1962. Throughout the twentieth century the study of crystalline molecules has continued to expand our knowledge by providing detailed structures of vitamins, proteins (enzymes, myoglobin, bacterial membranes), liquid crystals, polymers, and organic and inorganic compounds.

Today, crystals are still worn for decorative purposes in the form of gems and jewels; there are still believers in the mystical powers of crystals, but there is no scientific basis for any of the many claims made for them by "New Age" promoters. Crystals are used in modern technological applications, such as lasers.

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Science EncyclopediaScience & Philosophy: Cosine to Cyano group