Mineralogy

Mineralogy is the science that studies the chemical composition, crystal structure, and physical characteristics (e.g., hardness, magnetism, and optical properties) of minerals, as well as their genesis, transformation, and use by humans. The classification and nomenclature of minerals is codified by the International Mineralogical Association (IMA), composed of various organizations representing mineralogists in different countries.

It includes the following subdisciplines:

  • Descriptive Mineralogy: deals with the measurement and recording of physical properties that aid in the identification and description of minerals.
  • Crystallography: investigates the internal structure of crystalline substances.
  • Crystallochemistry: studies the relationships between chemical composition, internal structure, and physical properties.
  • Mineralogical classification: classification of all existing mineral species.
  • Geological distribution: characterization of the place of origin of minerals.

Historical notes

Early speculations, studies, and theories of mineralogy were written in ancient Babylon, the ancient Greco-Roman world, ancient and medieval China, and noted in the prana of Sanskrit texts of ancient India. However, the first systematic scientific studies of minerals and rocks were developed in post-Renaissance Europe. The credible study of mineralogy was founded on the foundations of crystallography and the microscopic study of rock sections with the invention of the microscope in the 17th century.

The interest in minerals is very ancient in the history of mankind. Minerals and rocks such as quartz, chalcedony, flints, quartzites were known by the most ancient cultures and used for the manufacture of tools and weapons; later, with the rise of the first historical civilizations, the usefulness of metalliferous minerals was understood and the search for stones used for jewelry and ornaments was intensified.

Minerals were considered primarily from the point of view of their usefulness: in the works of Greek and Roman scholars on minerals, which are, moreover, rather rare (especially interesting are the writings of Theophrastus, a disciple of Aristotle, and Pliny the Elder), there are descriptions of metalliferous deposits of gold, silver, lead, copper, tin, mercury and the related minerals and rocks that contain them, but there is a lack of mineralogical definitions and classifications, as well as very confused and fragmentary theories on the origin of minerals; for example, it was believed that quartz was formed by freezing very pure water.

Gems such as topaz, emeralds, rubies, aquamarines, garnets, were sought after both for their beauty and because they were attributed magical powers and therapeutic virtues from astral influences. This situation continued substantially throughout the Middle Ages until the beginning of the Renaissance.

Treaties and manuals of this period list the various species of minerals, generally in alphabetical order, describing the most striking features (color, transparency, morphology), or at most dividing them into minerals, metallic and not, and precious stones, listing for the latter the magical properties in accordance with the concepts and doctrines of alchemists. The only treatise that for its organicity and originality stands out from similar works dates back to the Arab Avicenna: in it is attempted a classification based on the chemical composition and is rejected the theory of the maturation of metals, according to which metals and their minerals with time would be transformed into purer and more noble substances: so lead would be gradually transformed into silver and then into gold.

During the Renaissance, the intense mining exploitation and the need to find new deposits and to use new extraction techniques brought a great impulse to the study of mineralogy. Dates back to this period the activity of Georg Bauer called Agricola (1494-1555), in whose works, in particular in De natura fossilium, faces the study of minerals with modern criteria, dividing them into simple bodies (earths such as clays, precious stones, building and ornamental stones, etc..) and in compound bodies (metalliferous minerals and aggregates of minerals distinguishable to the naked eye), taking into account the physical properties and within certain limits of the geometric form.

Notions of mineralogy are also found in the treatise Pyrotecnia by Vannoccio Biringuccio (1480-1539). In the seventeenth century mineralogy studies are oriented towards the attempt to explain the origin of minerals, generally considered as the deposit of saturated salt solutions, while new important morphological and optical properties are discovered and investigated. The most representative exponent of this direction is the Danish naturalist Stenone (1638-1686) to whom we owe original research in petrography and paleontology and the first partial statement of the law of constancy of dihedral angles.

Similar observations and results were achieved by Domenico Guglielmini (1655-1710), who also realized that there is a close relationship between the regular external shape of minerals and internal structure. In those years appeared the first major mineralogical classifications based on chemical composition: remarkable are in this respect the works of G. Wallerius, T.O. Bergman and M.V. Lomonosov, published in the mid-eighteenth century. A considerable progress in mineralogical studies was recorded towards the end of that century, mainly thanks to Romé de l’Isle and René J. Haüy. R. de l’Isle, taking up the theories of Stenone, enunciated the first law of crystallography supported by experimental observations carried out with the goniometer of application. To Haüy we owe instead the fundamental law of “rationality of indices” and the first theory on the internal structure of minerals understood as crystalline bodies resulting from the juxtaposition of elementary polyhedra (the so-called integrating molecules) having the shape of the solid of flaking.

Europe and the Middle East

The Ancient Greek writers Aristotle (384-322 B.C.) and Theophrastus (370-285 B.C.) were the first in the Western tradition to write about minerals and their properties, as well as to give a metaphysical explanation of them. The Greek philosopher Aristotle, in his “Meteorology,” theorized that all known substances were composed of the four elements water, air, earth, and fire, with the properties of dryness, moisture, heat, and cold. The Greek philosopher and botanist Theophrastus in his work De Mineralibus, accepted Aristotle’s point of view, and divided minerals in two categories: those affected by dryness and those affected by humidity.

The Aristotelian theory of metaphysical emanation and exhalation (anathumiaseis) included the first speculations on earth sciences, integrating mineralogy. According to this theory, while metals were supposed to freeze due to loss of moisture, dry gas exhalation (pneumatodestera) was the efficient material cause of minerals found in the earth’s soil. The philosopher postulated these ideas using the example of moisture on the Earth’s surface (a moist vapor “potentially like water”), while the others were ejected from the Earth itself, referring to the attributes of hot, dry, smoky, and highly combustible (“potentially like fire”). Aristotle’s metaphysical theory, from ancient times, had a great range of influence on similar theories formulated later in Europe, as historian Berthelot has noted:

The theory of exhalations was the starting point for later ideas about the generation of metals in the earth, which we meet with Proclus, and which reigned during the Middle Ages.

With philosophers like Proclus, the theory of Neoplatonism was also spread to the Islamic world during the Middle Ages, also forming a basis for metaphysical ideas about mineralogy in the medieval Middle East. Medieval Islamic scientists who dealt with these issues were many, including Persian scientists Ibn Sina (ابوعلى سينا/پورسينا) (980-1037 AD), who rejected alchemy and the primitive notions of Greek metaphysics about whether metals and other elements could be transformed into others. However, the idea of the slow change in chemical composition of the earth’s crust was widely held in the metaphysics of the ancient Greek world and in the medieval world. This context also includes the scientist Jabir ibn Hayyan (721-815 AD), the first to bring the experimental method to alchemy. Aided by Pythagorean mathematics, he discovered the method of synthesis for hydrochloric acid, nitric acid, and methods for distillation and crystallization (the latter two were essential to the understanding of modern mineralogy).

Pliny the Elder

Ancient Greek mineralogical terminology has been passed down for centuries, with widespread use in modern times. For example, the Greek word ῾ἀσβεστος (asbestos with the meaning of “unquenchable, unquenchable”), is used to refer to asbestos because of the unusual appearance of this natural material due to the fibrous structure of the minerals that compose it (chrysotile, in particular, which is one of the polymorphic modifications of serpentine).

Among the earliest naturalists Strabo (58 B.C.-25 AD) and Pliny the Elder (23-79 AD) both wrote about asbestos, its qualities, and its origins, with the Hellenistic belief that it was a type of vegetable. Pliny the Elder listed it as a common vegetable in India, while historian Yu Huan (239-265 AD) in China listed this ‘fireproof rag’ as a product of ancient Rome or Arabia (Chinese: Daqin).

Although the documentation of these minerals in ancient times does not reach that of modern scientific classification, there were nevertheless extensive writings on mineralogy. For example, Pliny devoted 5 entire volumes of his work Naturalis Historia (AD 77) to the classification of “lands, metals, stones, and gems.” However, prior to the works that decreed the final establishment of mineralogy in the 16th century, the ancients recognized no less than 350 minerals to be listed and described.

Giorgio Agricola, father of Mineralogy

In the early 16th century, the writings of the German scientist Georg Bauer, signed Georgius Agricola (1494-1555) in his Bermannus, sive de re metallica dialogus (1530) are considered to be the foundational writings of mineralogy in the modern sense of their study. Agricola wrote the treatise as a city physicist, and doing experiments in Joachimsthal, which was then a center rich in industrial metallurgical mines and foundries. In 1544, he published his written work De ortu et causis subterraneorum, which is considered to be a milestone for modern physical geology.

In his work (in much the same way as Ibn Sina) Agricola strongly criticized the theories held by ancient Greek philosophers such as Aristotle. His work on mineralogy and metallurgy continued with the publication of De veteribus et novis metallis in 1546, and culminated in his best known work, the De re metallica of 1556. It was an impressive work in which issues relating to the extraction, refining, and smelting of metals were explicated, flanked by discussions of the geology of mineral deposits, topography, and the construction of mines and their ventilation. For the following two centuries this written work remained the most authoritative text on mining in Europe.

Agricola developed many mineralogical theories on the basis of practical experience, including an understanding of the concept of deposit channels, formed by the circulation of ground water in fissures that follows the deposition of surrounding rocks. As will be noted below, medieval Chinese mineralogy had previously developed this type of concept.

For his work, Agricola has been made known to posterity as the Father of Mineralogy.

After the seminal works written by Agricola, the work Gemmarum et Lapidum Historia by Anselmus de Boodt (1550-1632) of Bruges is widely recognized by the scientific community as the first definitive work on modern mineralogy. German mining chemist Johann Friedrich Henckel wrote his 1760 Flora Saturnisans, which was the first treatise in Europe to deal with geobotanical minerals, although the Chinese had mentioned these concepts in earlier treatises from 1421 and 1664. In addition, the Chinese writer Du Wan made clear references to the relationship between precipitation and erosion relationships in his 1133 work Yun Lin Shi Pu, prior to Agricola’s 1546 work.

China and the Far East

In ancient China, the earliest literary list of minerals can be traced back to at least the 4th century BC, with the book Ji Ni Zi listing 24 minerals. The Chinese idea of metaphysical mineralogy dates back at least to the ancient Han dynasty (202 B.C.-220 A.D.). Since the 2nd century BC text of Huai Nan Zi, the Chinese have used terms of ideological Taoism to describe meteorology, precipitation, the different types of minerals, metallurgy, and alchemy. Although the understanding of these concepts in Han times was Taoist in nature, the theories proposed were similar to those formulated by Aristotle in his theory of mineralogical exhalations (described above).

As of 122 B.C.E., the Chinese had therefore formulated the theory for the metamorphosis of minerals, although some historians such as Dubs have noted that the tradition of Chinese alchemical-mineralogical doctrine leads back to the School of Naturalists led by the philosopher Zou Yan (305 B.C.-240 B.C.E.). Within the broad category of rocks and stones (shi) and metals and alloys (jin), by Han’s time the Chinese had hundreds (if not thousands) of types of stones and minerals listed, as well as many theories about their formation.

In the 5th century AD, Prince Qian Ping Wang of the Liu Song Dynasty wrote in the encyclopedia Tai-ping Yu Lan (circa 444 AD, from the lost book Dian Shu, or Management of All Techniques):

The most precious things in the world are stored in the innermost region of all. For example, there is orpiment. After one hundred years it changes to realgar. After another hundred years realgar changes to yellow gold.

In ancient medieval China, mineralogy became firmly linked to empirical observations in pharmaceutics and medicine. For example, the famous watchmaker and mechanical engineer Su Song (1020-1101) of the Song Dynasty (AD 960-1279) wrote about mineralogy and pharmacology in his work Ben Cao Tu Jing in 1070. In his writing, he created a systematic approach to list various different minerals and their use in medicinal mixtures, such as all the various known forms of mica that can be used to treat various digestive problems.

Su Song also made considerations about the subconcoid fracture of native cinnabar, signs of mineral deposit beds, and provided descriptions of the shape of the minerals. Similar to the mineral strands formed by the circulation of soil water mentioned above about the German scientist Agricola, Su Song made statements concerning copper carbonate, as Ri Hua Ben Cao had done earlier in 970 AD with copper sulfate.

Yuan Dynasty scientist Zhang Si-xiao (d. 1332) wrote a groundbreaking treatise on the conception of mineral deposits from the circulation of water in the soil and rock fissures, two centuries before Georgius Agricola came to similar conclusions. In his work Suo-Nan Wen Ji, he applied this theory in describing the deposition of minerals by evaporation of (or by precipitation from) soil waters into strands of minerals.

In addition to the alchemical theories already mentioned, later Chinese writers such as Ming Dynasty physicist Li Shizhen (1518-1593) put in writing some theories of mineralogy similar to Aristotle’s metaphysical theories, as he wrote in the pharmaceutical treatise Běncǎo Gāngmù (本草綱目, Compendium of Materia Medica, 1596). Another Ming-era figure, the famous geographer Xu Xiake (1587-1641) wrote about mineralogical and mycascist deposits in one of his treatises.

However, while European literature on mineralogy became wide and varied, writers of the Ming and Qing dynasties wrote little on the subject (even compared to what had been produced during the Song era). The only other works of note composed in these two eras are Yu Jun’s Shi Pin (Hierarchy of Stones) of 1617, and Song Luo’s Guai Shi Lu (Strange Rocks) of 1665, and Guan Shi Lu (On the Observation of Rocks) of 1668. A notable figure in the Song Dynasty is Shen Kuo.

The theories of Shen Kuo

The statesman and scientist of China’s medieval Song dynasty, Shen Kuo (1031-1095) wrote his own theory of land formation, which included some aspects of mineralogy.

In his work Meng Xi Bi Tan (梦溪笔谈; in English Dream Pool Essays, 1088), Shen formulated hypotheses about the processes that presided over land formation (geomorphology); these theories were based on observations of fossil sea shells in a geological layer in the Taihang Mountains, hundreds of kilometers away from the Pacific Ocean. He inferred that the earth was formed by mountain erosion and silt deposition, and then described erosion, sedimentation, and uplift. In an early work of his (circa 1080), he wrote of a curious fossil of an apparently marine creature found far inland. It is also interesting to note that the contemporary author of the work Xi Chi Cong Yu attributed the idea of particular places under the seas where snakes and crabs were petrified to a Wang Jinchen.

With Shen Kuo’s writings on the discovery of fossils also came a hypothesis about climate changes with the passage of time. The reasons for these assumptions lay in the discovery of hundreds of petrified bamboos in a dry climate zone in northern China, when a huge avalanche on a riverbed revealed them. Shen theorized that in prehistoric times, the climate of Yanzhou must have been very wet and humid like that of southern China, where bamboos find an ideal growing climate.

Similarly, historian Joseph Needham compared Shen’s theories with those of Scottish scientist Roderick Murchison (1792-1871), who was inspired to become a geologist after observing a providential avalanche. Moreover, Shen’s description of sedimentary depositions predates that of James Hutton, who wrote his groundbreaking work (considered the cornerstone of modern geology) in 1802. The influential philosopher Zhu Xi (1130-1200) also wrote about curious natural phenomena such as fossils, and had read Shen Kuo’s works.

Modern mineralogy

Throughout the nineteenth century the study of mineralogy followed two distinct directions in direct relation to the contemporary advances in chemistry and physics: on the one hand mineralogy was identified almost with mineralogical chemistry, on the other hand with crystallography. The main results of the chemical address were the exact determination of the composition of the minerals already known and of the many other species that naturalists and geologists collected during their research on the ground, and the discovery of the phenomena of polymorphism and isomorphism, made by E. Mitscherlich.

Crystallographic studies continued especially by Bravais, Sohnke and Fedorov who clarified the reticular structure of crystals, thanks also to the study of optical properties of minerals made possible by the invention of polarizing prisms by W. Nicol. The confirmation of the accuracy of crystallographic knowledge came from the research and experience of Max von Laue in collaboration with Friedrich and Knipping on X-ray diffraction (1912), obtained using crystals as fine lattice.

The need to define the nature of lattice nodes had as a consequence to converge and reunite the two sectors in which mineralogy was divided: in fact appeared evident the close relationship between composition, chemical and physical properties and lattice structure of crystalline minerals. The current studies of mineralogy use to determine these relationships the most recent theoretical and experimental progresses of chemistry and crystallographic physics (differential thermal analysis, spectrographic analysis with X-rays, etc..); of more recent development are the experimental researches that try to reproduce in laboratory the processes of natural minerogenesis and petrogenesis.

More recently, driven by advances in experimental techniques (such as neutron diffraction) and the availability of computational power (the latter has allowed the elaboration of very accurate atomic-scale simulations of crystal behavior), science has begun to examine more general problems related to inorganic chemistry and solid-state physics.

The latter, however focuses its study on crystal structures commonly encountered in rock-forming minerals (such as perovskites, clay minerals, and silicate structures). In particular, great strides have been made in this field in understanding the relationships between the atomic-scale structure of minerals and their functions; in nature, prominent examples might be accurate measurements and predictions of the elastic properties of minerals, which have led to an in-depth look at the seismological behavior of rocks and deep discontinuities in Earth’s mantle seismograms. To this end, in their focus on the connection between atomic-scale phenomena and macroscopic properties, mineral sciences (as they are now commonly known) show perhaps more overlap with materials science than any other discipline.

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