Mineralogy

History and Advances in Mineralogy

• Early writing on mineralogy comes from ancient Babylonia, the ancient Greco-Roman world, ancient and medieval China, and Sanskrit texts from ancient India and the ancient Islamic world.
• Books on the subject included the 'Natural History' of Pliny the Elder and 'Kitab al Jawahir' by Persian scientist Al-Biruni.
• Georgius Agricola wrote works such as 'De re metallica' and 'De Natura Fossilium' which began the scientific approach to mineralogy.
• Nicholas Steno observed the law of constancy of interfacial angles in quartz crystals in 1669.
• Jöns Jacob Berzelius introduced a classification of minerals based on their chemistry in 1814.
• Advances in experimental technique and computational power have led to significant progress in mineralogy.
• The science has branched out to consider more general problems in inorganic chemistry and solid-state physics.
• The field has made great advances in understanding the relationship between atomic-scale structure of minerals and their function.
• Accurate measurement and prediction of the elastic properties of minerals have provided new insights into seismological behavior.
• The mineral sciences display overlap with materials science in their focus on the connection between atomic-scale phenomena and macroscopic properties.

Physical Properties and Crystal Structure

• Physical properties of minerals can be measured on a hand sample.
• Properties include density, mechanical cohesion (hardness, tenacity, cleavage, fracture, parting), visual properties (luster, color, streak, luminescence, diaphaneity), magnetic and electric properties, radioactivity, and solubility in hydrogen chloride (HCl).
• Hardness can be determined using the Mohs scale or measured on an absolute scale using a sclerometer.
• Tenacity refers to the way a mineral behaves when broken, crushed, bent, or torn.
• Cleavage is the tendency to break along certain crystallographic planes.
• The crystal structure is the arrangement of atoms in a crystal.
• It is represented by a lattice of points which repeats a basic pattern called a unit cell in three dimensions.
• The lattice can be characterized by its symmetries and the dimensions of the unit cell.
• There are 32 possible crystal classes and 230 possible space groups.
• X-ray powder diffraction is used to analyze the crystal structures of minerals.

Crystallography and Optical Properties

• Crystallography is the study of crystals and their structure.
• The lattice remains unchanged by certain symmetry operations such as reflection, rotation, inversion, and rotary inversion.
• Translation, screw axis, and glide plane are operations that displace all the points in the lattice.
• Most geology departments have X-ray powder diffraction equipment for crystal structure analysis.
• X-rays have wavelengths similar to the distances between atoms, allowing for diffraction patterns.
• Minerals have properties that require a polarizing microscope to observe.
• When light passes into a transparent crystal, it can be reflected or refracted.
• Crystals in the cubic system are isotropic, meaning their refractive index does not depend on direction.
• Other crystals are anisotropic, causing light to be broken up into two plane polarized rays.
• A polarizing microscope uses two plane-polarized filters to observe the polarization changes caused by anisotropic samples.

Chemical Elements and Analysis

• Some minerals are chemical elements, such as sulfur, copper, silver, and gold.
• Wet chemical analysis is a classical method for identifying composition, involving dissolving a mineral in an acid like hydrochloric acid.
• Elements in solution can be identified using colorimetry, volumetric analysis, or gravimetric analysis.
• Atomic absorption spectroscopy is a faster and cheaper method for chemical analysis, involving vaporizing the solution and measuring its absorption spectrum.
• Other techniques for chemical analysis include X-ray fluorescence, electron microprobe analysis, atom probe tomography, and optical emission spectrography.

Formation Environments and Biomineralogy

• Minerals can form in diverse environments, ranging from high temperature and pressure in the Earth's crust to low temperature precipitation on the Earth's surface.
• Possible methods of formation include sublimation from volcanic gases, deposition from aqueous solutions, crystallization from magma or lava, recrystallization due to metamorphic processes, and crystallization during diagenesis of sediments.
• Minerals can also form through oxidation and weathering of rocks exposed to the atmosphere or within the soil environment.
• The formation environment influences the composition, structure, and properties of minerals.
• Biomineralogy explores how plants and animals control and replace minerals under biological processes.
• Isotopic studies and chemical mineralogy techniques are used to study growth forms in living organisms and determine the mineral content of fossils.
• Mineral evolution is a new approach that investigates the co-evolution of the geosphere and biosphere, including the role of minerals in the origin of life and organic synthesis.
• Biomineralogy bridges the fields of mineralogy, paleontology, and biology.
• It provides insights into the interactions between living organisms and minerals.

Mineralogy Data Sources