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