Definition of a Mineral • A mineral is a naturally occurring, • homogeneous solid with a Physical Properties of Minerals • definite, but not fixed, composition, and Color, shape, density, • an ordered atomic arrangement that is hardness, etc • formed by inorganic processes. • A mineral is a natural, crystalline phase. Form and Habit Terms Each mineral species has (Crystal Growth Forms) unique and identifiable • Prismatic (well developed prism physical properties. faces) (Pyramidal) • Form and habit (Shape) • Columnar (Irregular prism faces) • Luster • Acicular (needle-like) • Color and Streak • Botryoidal (rounded growth surface) • Cleavage and Fracture • Tabular (Platey) • Hardness • Stellate (Radiating) • Density • Fibrous (fibers, asbestiform) • Tenacity • Dendritic (tree-like) Acicular Fibrous 1 Dendritic Dendritic Radiating Radiating Bladed Botryoidal 2 Prismatic Luster and Transparency • Luster • Transparency – Metallic – Opaque – Resinous – Translucent (waxy) – Transparent – Pearly – Greasy – Adamantine – Vitreous Metallic Adamantine Color and Streak • The reflectance color of minerals is strongly affected by transition metals (V, Cr, Mn, Fe, Co, Ni, and Cu). (Also rare earths) Vitreous Pearly • Color in hand specimen may not be diagnostic. • Color in streak generally indicates presence of iron or other transition metals. Chatoyance, Asterism, Asterism: Star Sapphire and Luminescence • Chatoyance and asterism are optical effects due to diffraction of light from small inclusions. • Luminescence is emission of light. – Visible or UV (black light) – Tribo-luminescence: glow when rubbed – Cathodo-luminescence is emission of light from electron bombardment 3 Cleavage and Fracture Hardness What scratches what? • Crystals tend to break on planes of • 1. Talc 6. Orthoclase weakness. • 2. Gypsum 7. Quartz – Cleavage: perfect – Parting: irregular • 3. Calcite 8. Topaz – Hackly: very irregular • 4. Fluorite 9. Corundum – Conchoidal Fracture: no cleavage, • 5. Apatite 10. Diamond breaks like glass. Density Tenacity: How does it deform? • Density units are g/cm3 (water is 1.0) • Densities range from 0.92 for ice to • Brittle: Fractures (quartz) ~1.8 for some zeolites to 22 for Os. • Most silicates are 2.5 to 3.5. • Ductile: Malleable (gold) • Most sulfides are 4.5 to 6.0 • Iron metal is ~8 • Sectile: Cut with a knife (mica) • Lead is ~13 • Gold and platinum are 19-22. Other Properties Unique Properties • Optical (Index of refraction) • Optical (Birefringence) • Ferro-magnetism • Optical (Spectroscopy) • Taste (Don’t do it. It might be • Chemistry (X-ray and electron witherite.) fluorescence) • Radioactivity (U and Th minerals) • X-ray diffraction (+ electron and • UV Fluorescence neutron) • Piezoelectricity (acentric crystals) • Other spectroscopies • Pyroelectricity (acentric crystals) – IR Raman (visible) – Mössbauer() Auger (electron) 4.