Friedrich Mohs
Friedrich Mohs was a notable German mineralogist, born on January 29, 1773, in Gernrode, Germany. He pursued studies in mathematics, physics, and chemistry at the University of Halle, later honing his expertise in mineralogy under the mentorship of Abraham Gottlob Werner at the Mining Academy in Freiberg. Mohs’s most significant contribution to the field of mineralogy is the Mohs scale of mineral hardness, developed during his tenure as a professor in Graz, Austria. This scale, which ranks ten minerals based on their ability to scratch one another, ranges from talc at 1 (softest) to diamond at 10 (hardest). Mohs's emphasis on physical characteristics for identifying minerals marked a shift from the chemical composition approach that dominated the era. His work laid the foundation for future advancements in mineral hardness testing, influencing subsequent methods used in material science. Mohs's legacy endures, as the Mohs scale is still utilized in various applications today, demonstrating its lasting impact on geology and mineralogy. He passed away on September 29, 1839, while traveling in Italy.
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Friedrich Mohs
German geologist and mineralogist
- Born: January 29, 1773; Gernrode, Germany
- Died: September 29, 1839; Agordo, Italy
Nineteenth-century German geologist/mineralogist Friedrich Mohs developed a system for classifying minerals based upon their physical characteristics. This method is still in use today.
Also known as: Carl Friedrich Christian Mohs
Primary field: Earth sciences
Specialty: Geology
Early Life
Carl Friedrich Christian Mohs was born in Gernrode, Germany on January 29, 1773. His father was a merchant.
Mohs attended the University of Halle, where he studied mathematics, physics, and chemistry. He also studied mechanics at the Mining Academy at Freiberg, Saxony. While at Freiberg, Mohs studied under German mineralogist and geognostician Abraham Gottlob Werner. Werner inspired Mohs’s interest in mineralogy, and the geological study of minerals.
Life’s Work
In 1801, at the age of twenty-eight, Mohs moved to Austria to become a foreman at the Neudorf/Harz Mine. Mohs took a position as curator for the private mineral collection belonging to wealthy banker, J. F. van der Null in 1802. As part of his responsibilities, he identified the minerals in the collection.
In 1812, Archduke Johann appointed Mohs Professor of Mineralogy at the Joanneum in Graz, a museum and science academy. It was during his time at Graz that Mohs finished the development of his scale of hardness for the identification of minerals.
Although most mineralogists of the era used chemical composition to categorize minerals, Mohs settled on hardness as one of the physical characteristics most helpful for classifying minerals. At the time, the use of physical traits in attempts to identify and categorize objects and life forms was widely popular among botanists and zoologists. His system was based on geometrical relationships that he derived from natural mineral forms.
Mohs organized the characteristics into what became known as the Mohs scale of mineral hardness. This scale ranks minerals between 1 and 10. Talc, with its very soft structure, is ranked at a 1. Diamonds, with their extremely hard surface, are ranked at a 10. The minerals in between are gypsum (2), calcite (3), fluorite (4), apatite (5), orthoclase (6), quartz (7), topaz (8), and corundum (9). These ten minerals form the standard measurements against which all other minerals and samples are compared.
The Mohs scale is a relative scale. It employs the comparison of minerals against other minerals to determine the hardness of a new specimen. Other characteristics of the specimen can also be used for identification, often in conjunction with the Mohs scale. Some of these other physical properties helpful for mineral identification and classification are luster, cleavage, crystalline form, and color. When taken together, these physical characteristics will help define the type of mineral to which any given specimen belongs.
According to the Mohs scale, a mineral with a higher number can scratch a mineral with a lower number. Therefore, calcite can scratch gypsum and talc. Topaz can scratch quartz, orthoclase, apatite, fluorite, calcite, gypsum, and talc. Nothing is capable of scratching the surface of a diamond, other than another diamond. By taking the sample minerals into the field, a geologist can determine what sort of specimens they find by seeing which mineral is capable of scratching the surface of the other.
Between 1815 and 1825, Mohs worked with German scientist Christian Weiss on the development of the major crystal systems. After Werner’s death in 1817, Mohs took his place as an instructor at the Mining Academy in Freiberg. He accepted an appointment as Professor of Mineralogy at the University of Vienna in 1826. In 1934, Mohs held both the custodianship of the Imperial Mineralogical Cabinet and a professorship at the University of Vienna.
In 1835, Mohs left the Imperial Mineralogical Cabinet to become mining counselor at the Mining University in Leoben, Austria. He died on September 29, 1839, during a trip to Agordo, Italy.
Impact
The Mohs scale of mineral hardness remains in use today. Although the notion of comparing and classifying hardness in minerals has existed since antiquity, Mohs’s work on the subject laid some of the groundwork for other scientists who later expanded on techniques for examining mineral hardness. Methods of measuring mineral hardness that came to light after Mohs’s death include the Brinell scale, the Vickers hardness test, and the Knoop hardness test.
Bibliography
Nesse, William D. Introduction to Mineralogy. Oxford: Oxford UP, 2011. Print. Discusses optical mineralogy, with a focuses on describing minerals in their geologic context. Includes an overview of crystallography.
Szymanski, Andrzej M., and Janusz Mikolaj Szymanski. Hardness Estimation of Minerals, Rocks and Ceramic Materials. Warsaw: PWN-Polish Scientific, 1990. Print. Offers an overview of hardness measurement methods, noting their comparative values and limitations. Also features extensive references for further reading on the subject.
Whitney, Donna L, Annia K. Fayon, Margaret E. Broz, and Robert F. Cook. “Exploring the Relationship of Scratch Resistance, Hardness, and Other Physical Properties of Minerals Using Mohs Scale Minerals.” Journal of Geoscience Education 55.5 (2007): 56. Print. Examines the relationships of the physical properties used to identify minerals using the Mohs Scale of Mineral Hardness.