A polymorph of quartz, has lower symmetry than quartz (I2/a) and a triclinic superstructure commonly occurs. The structure was described by Miehe and Graetsch (1992) as comprised of sections of right- and left-handed quartz alternating at the unit cell level to form a framework of corner sharing tetrahedra. The framework has 4-, 6- and 8-fold rings, and there is no open tunnel as found in alpha quartz. The nanoscale alternation follows the Brazil twin law, but because it is periodic at the unit cell level, moganite represents a (metastable) mineral phase. Moganite occurs as intergrowths with (alpha) quartz in chert, quartzine, flint, and chalcedony, thus indicating that these latter varieties are not minerals, but rock names. Any H₂O present in moganite is not structurally required.

Mohr’s circle is a two-dimensional graphical representation of the three-dimensional state of stress of a soil element subject to load in the normal stress – shear stress coordinate system. Components (i.e., orientations of the normal and shear stresses) of applied stress may be graphically obtained across various inclined planes at a given point in a stressed body.
Syn., Mohr circle of stress, stress circle

Mohs’ scale of hardness is composed of a series of common minerals with increasing hardness: (1) talc, (2) gypsum, (3) calcite, (4) fluorite, (5) apatite, (6) orthoclase, (7) quartz, (8) topaz, (9) corundum, and (10) diamond. Hardness is determined by a scratch test, as minerals of greater or equal hardness can scratch those of equal or lesser hardness.
Cf., hardness, Vickers hardness

The number of moles of solute per kilogram of solvent. Because weights of a solute/solvent are generally fixed at all temperatures, this scale is useful for experiments where physical properties (e.g., boiling point, freezing point) are examined over a temperature range.
Cf., molarity, formality, normality, mole fraction

The number of moles of the solute in one liter of solution. Useful where experiments use measured volumes and where temperature effects are not being studied.
Cf., formality, normality, molality, mole fraction

Number of moles of one component divided by the total number of moles of all components.
Cf., molarity, formality, normality, molality

A molecular simulation for calculating time-averaged properties of a molecular system. The model system is simulated by solving Newton’s equations of motion, including kinetic and potential energy terms. The energy terms can be obtained by using classical (force field) or quantum (Density Functional Theory) methods. System constraints (e.g., constant volume, temperature, pressure) usually correspond to a thermodynamic ensemble.
Cf., density functional theory, force field, Grand Canonical Monte Carlo simulation, Monte Carlo molecular simulation, quantum calculation

A method of calculating the electronic structure and related properties of a finite molecular system consisting of two or more atoms by solving the Schrodinger equation to determine the electronic structure. Various methods exist to approximate the simultaneous solution of the Schrodinger equation for all electrons in the molecular system.

A set of computational methods used to calculate physical or chemical properties of a model system consisting of atoms or molecules. Computed properties can include chemical reactions, structure, spectroscopy, and transport. Many techniques exist for such simulations based on model system size and desired accuracy, from quantum methods to classical (force field) methods.
Cf., force field, quantum calculations

the number of reacting molecules, atoms, or ions in a single-step chemical reaction. For example, a unimolecular reaction may involve radioactive decay of a single atom, or one molecule producing other molecules. A bimolecular reaction involves the collision and reaction between two molecules, atoms or ions to form other products. Cf., Transition State Theory