A Brief History of Crystals
Probably the first historical references to the use of crystals come from the Ancient Sumerians (4th millennium BC), who included crystals in magic formulas. Crystals were (and are) also used for healing in traditional Chinese Medicine, which dates back to at least 5000 years.
The Ancient Egyptians used lapis lazuli, turquoise, carnelian, emerald and clear quartz in their jewelry. They used some stones for protection and health, and some crystals for cosmetic purposes, like galena and/or malachite ground to a powder as the eye shadow. Green stones in general were used to signify the heart of the deceased and were included in burials, as it was also found at a later period in Ancient Mexico.
The Ancient Greeks identified quartz with the word “crystal” (κρύσταλλος, crustallos, or phonetically kroos’-tal-los = cold + drop), that is, very cold icicles of extraordinary hardness. Theophrastus (c. 371 – c. 287 BC), in his treatise On Stones (Περὶ λίθων), which was used as a source for other lapidaries until at least the Renaissance, classified rocks and gems based on their behavior when heated, grouping minerals by common properties, such as amber and magnetite, which both have the power of attraction.
Probably the first reference to crystals in Ancient Rome was reported by Pliny the Elder (I Century AD) in his “Natural History”, where he describes the windows and greenhouses of the richer inhabitants of the Roman Empire being covered by crystals of “Lapis specularis”, the Latin name for large transparent crystals of gypsum. This dihydrated form of calcium sulphate was extracted by Romans in Segóbriga (Spain) because of its crystal clarity, size (up to one meter) and perfect flatness.
An important part of the economy of the Roman Hispania during the first century AD was based on the mining of this mineral and its distribution through the commercial road that was established (click on the image on the right), transporting this mineral in carts pulled by oxen to the port of Cartagonova for its commercial distribution throughout the Roman Empire.
The vast amount of mineralogical information contained in Pliny’s “Natural History” was preserved and enhanced in “Book XVI on Stones and Metals” which covered the “Etymologiarum” of Isidor of Seville (560-636). It is also preserved in the “Lapidarium” of Alfonso X (1221-1284), a fascinating work by a group of Muslim, Hebrew and Christian sages from a time when peaceful multicultural collaboration was demonstrated to be possible.
Ibn Sīnā “Avicenna” (980-1037), polymath of Persian origin who wrote about 450 books, mainly in philosophy and medicine, classified some minerals by their chemical composition. Vannoccio Biringuccio (1480-1539), Italian metallurgical, associated shapes and angles with certain minerals, and Georg Bauer “Georgius Agricola” (1494-1555), considered the father of mineralogy, made the first classification of minerals based on their physical properties.
However, it was the unparalleled talent of the Arabian geometers in investigating the problem of tessellation of two-dimensional space, which made the most important pre-Renaissance Spanish contribution to crystallography and geometrical art. The decorative symmetry of the tiling in the Alhambra Palace in Granada (Spain) is used today to teach symmetry all over the world.
The German mathematician, astronomer and astrologer Johannes Kepler (1571-1630) marveled when a snowflake landed on his coat showing its perfect six-cornered symmetry. In 1611 Kepler wrote ”Six-cornered Snowflake” (Latin title ”Strena Seu de Nive Sexangula”) the first mathematical description of crystals. In this essay, the first work on the problem of crystal structure, Kepler asks: Why do single snowflakes, before they become entangled with other snowflakes, always fall with six corners? Why do snowflakes not fall with five corners or with seven? Despite its modest size, Kepler’s essay is remarkably rich in ideas. One of his major discoveries was the geometry of the packing of spheres (the well known principle of closest packing in modern structural crystallography). He dealt with the densest cubical packing, and although he was not aware of the densest hexagonal packing, Kepler described two less dense packings for spheres, the hexagonal and the simple cubic. Moreover, starting from the spherical packings, Kepler drew conclusions about the parallelohedra, the convex polyhedra which can fill space in a regular manner, anticipating the conclusions of R.J. Haüy (1784) and E.S. Fedorov (1885). Kepler’s work contains indirect pointers to the Law of Constant Angles for a six-sided snow crystal. Thus one can consider Kepler as a forerunner of the discoverers of this law (N. Steno, 1669; M.W. Lomonosov, 1749; Romé de l’Isle, 1783).
In addition to Kepler’s work, the greatest contribution to crystallography, paleontology, and geology made during the 17th century was made by the Danish catholic bishop and scientist Nicolaus Steno (in Danish Niels Stensen, 1638-1686) who became professor of anatomy at the University of Padua in Italy, and where he was appointed house physician to Grand Duke Ferdinand II of Tuscany (1610-1670). During this decade he made his greatest contributions to science. In Stensen’s work “De Solido Intra Solidum” he observed for the first time the fundamental crystallographic Law of the Constancy of Interfacial Angles. Using drawings and two brief sentences, Stensen remarked that although crystals of quartz (silicon oxide) and hematite (iron oxide) appear in a great variety of shapes and sizes, the same interfacial angles persisted in every specimen. This observation, the Law of Constancy of Angles, was confirmed and shown to be true for crystals of many other substances by Romé de l’Isle (1736-1790), after more than a hundred years later, in 1783. Moreover, Stensen discussed the growth of crystals in a fluid medium, but for him, this was only a special case illustrating the main problem of the book: How are solids of all kinds formed in nature? His answer was: if a solid body has been produced according to the laws of nature, it has been produced from a fluid … either immediately from an external fluid, or through one or more mediating internal fluids. At that time internal fluids accounted for the growth of animals and plants; sedimentation, incrustation, or crystallization from external fluids explained the formation of rocks and minerals. It seems obvious that Stensen’s observations on the growth of crystals were also very important to crystallography.
The French mineralogist Jean-Baptiste Louis Romé de l’Isle (1736-1790) can be considered as one of the creators of modern crystallography. He was the author of “Essai de Cristallographie” (1772), the second edition of which, regarded as his principal work, was published in 1783 as “Cristallographie” in three volumes and an atlas. His formulation of the Law of Constancy of Interfacial Angles was built on the observations by Nicolaus Steno (Niels Stensen). However, the definitive solid pillar in the construction of crystallography was set up by the Abbé Haüy (René Just Haüy, 1743-1822), professor of the humanities at the University of Paris, during the last decades of the 18th century. The theory of crystal structure elaborated by Haüy (“Essai d’un Théorie sur la Structure des Cristaux”, 1784), based on his discourses on laws of Symmetry, of Rational Intercepts, and of Constancy of Crystalline Form, does not differ substantially, in its essential points, from the views prevailing nowadays. By the way, a collection of crystallographic solids given by Haüy to the Galician mathematician José Rodríguez González (1770-1824) was used by the crystallographers Augusto González de Linares (1845-1904) and Laureano Calderón Arana (1847-1894) who established what probably was the first (1888) Chair of Crystallography in a European University (Santiago de Compostela).
The previous observations and the mathematical developments introduced during the 19th Century brought us to the modern structural crystallography…
In 1830 the German physician Johann Friedrich Christian Hessel (1796-1872) proved that, as a consequence of Haüy’s Law of Rational Intercepts, morphological forms can combine to give exactly 32 kinds of crystal symmetry in Euclidean space (32 point groups), since only two-, three-, four-, and six-fold rotation axes can occur. In 1848 the French physicist Auguste Bravais (1811-1863) discovered that there are 14 unique lattices (Bravais lattices) in three dimensional crystalline systems, correcting the previous scheme (15 lattices) conceived by the German Moritz Ludwig Frankenheim (1801-1869) three years before.
Finally, the 14 Bravais lattices and the 32 point groups were the constraints between which the eminent Russian crystallographer Evgraf S. Fedorov (1853-1919), and independently the German mathematician Arthur Schoenflies (1853-1928), deduced in 1890-1891 the 230 possible space groups that restrict the mutual arrangement of building units (atoms, ions, molecules) inside crystals.