University:
Michigan State University
Course:
GLG 321 | Mineralogy and Geochemistry
Academic year:

2022
Views:

178

Pages:

4
Author:

ilikemyicons0y5

Physical Properties of Minerals • Color • Hardness (Moh’s scale) • Luster • Fluorescence • Transparency • Magnetism • Habit • Reactivity or solubility • Crystal morphology/symmetry • Radioactivity • Cleavage, fracture, parting • Odor, feel, taste • Streak color • Density • Inclusions, exsolutions, alteration Properties – Transparency • Transparent: Visible light passes through the material • Translucent: Visible light passes through, though not all light is transmitted. • Opaque: No light goes through. Transparent calcite showing double refraction Translucent ulexite Opaque hematite Properties – Color • Color in minerals is caused by the selective absorption of certain wavelengths of visible light. • The major factors responsible for the production of color in minerals are: The presence of a color-causing (chromophore) element that is essential to the mineral composition The presence of a minor color-causing (chromophore) chemical impurity Crystal structure Crystal structure defects Inclusions of very fine impurities of another mineral or substance Directional optical effects caused by thin film interference due to fine lamellar intergrowths (e.g., labradorite) 1. 2. 3. 4. 5. 6. • First two are most common. Chromophore: An atom of group whose presence is responsible for the color of a compound. Color – Crystal Field Transitions • Transition metals (Ti, V, Cr, Mn, Fe, Co, Ni, Cu) have partly filled inner 3d orbitals • The electrons in these orbitals can be excited by energy in the visible spectrum. • The corresponding energy change equals the energy of light absorbed. Color – Charge Transfers • Transfers of electrons between O2- and metal cation, or between two metal ions of different charge separated by O2- can also cause color (e.g., purple in amethyst, blue in sapphire). Color – Color Centers • Caused by structural defects from a missing ion. changingmineral folor Color – Chromophore (Essential element) • “Olivine” (Forsterite-Fayalite series) • Fe2+ causes green color in lower concentrations, dark brown in high concentrations 80% Typical mantle olivine ~ Mg1.6Fe0.4SiO4 “End-member” Forsterite Mg2SiO4 (J. McAvoy photo) “End-member” Fayalite Fe2SiO4 (R. Luetcke photo) Color – Chromophore (Minor/trace element) • Single elements: For example Cr3+ substituting for Al3+ in red spinel (MgAl2O4) Khan 901

Physical Properties of Minerals

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