Physical Properties: Reference Chapter 3: Mineralogy by Dexter PerkinsCrystal Shape: form and habitBoth habit and form are extremely diagnostic in identifying minerals.Habit: TermsEuhedral, Subhedral, AnhedralSimple or Contact twins: e.g. the fish tail of gypsumMany minerals tend to break along twin planes. When this occurs it is called PARTING.FRACTURE:Conchoidal: quartzSPECIFIC GRAVITYWeight Air/(Weight Air-Weight in water) = specific gravityCOLOR AND STREAKPlay of Colors: Iridescence--For example, plagioclase  labradoriteLUSTERMetallic or non-metallicNon-metallic: vitreous or glassy; silky; resinous; pearly; greasy; waxy, dull; earthyLUMINESCENCEMAGNETISMMagnetite and PyrrhotiteTENACITYThe resistance of a mineral to breaking: brittle, malleable, sectile, ductile, flexible and elastic.OTHERSReaction to HCl.Physical Properties: Reference Chapter 3: Mineralogy by Dexter PerkinsCrystal Shape: form and habitHabit refers to the overall shape of a crystal or aggregate of crystals. In other words, the appearance of single crystals, as well as the manner in which crystals grow together in aggregates.Form: to mineralogists this refers to a group of crystal faces related by the crystals symmetry. For example pyrite forms in cubes. Quartz forms in hexagonal prisms. Both habit and form are extremely diagnostic in identifying minerals.Habit: Terms1. Acicular--slender, needle-like crystals: tourmaline, hornblende, arsenopyrite, rutile, apatite, sillimanite2. Capillary and filiform: hairlike or thread-like: native Au, Ag, Cu3. Bladed--elongated crystals flattened like a knife blade: kyanite, tremolite4. Dendritic: arborescent, in slender divergent branches, somewhat plantlike--native metals, pyrolusite5. Radiating: divergent: zeolite; tremolite; talc6. Drusy--surface covered with a layer of small crystals--sugar like calcite, quartz, sphalerite, pyrite7. Fibrous: aspect ratio 10:18. Globular and colloform: radiating individuals forming small spherical groupsbotryoidal-bunch of grapesreniform  kidney-likemammillary - very largezeolites, quartz, malachite, goethite, pyrolusite, hematite9. Foliated: easily separable into plates or leaves: tremolite; hematite; 11. Micaceous: similar to above but splits into very thin sheets: muscovite, biotite, chlorite12. Tabular or lamellar--flat and plate-like: barite, dolomite13. Granular--composed of many individual grains of similar size14. Prismatic or columnar elongated crystals with identical faces parallel to a common directionEuhedral, Subhedral, AnhedralTwinning Crystals that are related to one another by some geometric relation.Simple or Contact twins: e.g. the fish tail of gypsumPenetrative: e.g. Carlsbad or StaurolitePolysynthetic (multiple): PlagioclaseCyclic: aragoniteMany minerals tend to break along twin planes. When this occurs it is called PARTING.Polysynthetic Penetrative Cyclic SimpleCLEAVAGE AND PARTINGCleavage is the easy breakage of a mineral along a plane surface. The reason it occurs is the geometric arrangement of atoms in a mineral grain is generally such that a force of cohesion is lessalong some particular plane in the crystal lattice. A good example is the perfect cleavage in mica that is parallel to 001. (Note students generally become very confused about identifying crystal faces and cleavages--especially when some cleavages are parallel to particular crystal faces. (Galena for example--forms cubes and has cubic cleavage.))Perfect: Very good breakage and the new surfaces are shiny.Distinct: New surfaces broken by frequent irregular steps.Indistinct: Generally rough with only a few planar areas (generally not useful).Many minerals have more than one cleavage direction and this yields intersecting cleavage at various angles. These angles are very distinctive of minerals and are used to identify minerals. A good example is the 60/120 cleavage in hornblende and 87/93 cleavage in pyroxene. This is the only sure way to tell the minerals apart.FRACTURE:Fracture is the way a crystal breaks. Crystals that tend to have good cleavages, break along them first. In galena for example you may not see a fracture because the mineral has a tendency to break into cubes. Mica, however, has only one cleavage and you will see both fracture and cleavage. Terms that are used to describe fracture are:Conchoidal: quartzHackly: jagged and sharpFibrous and splinteryUneven or irregular: rough and irregular surfaces.HARDNESS  MOHS HARDNESS SCALEThis is a minerals resistance to scratching. It is a relative scale. Minerals with higher numbers will scratch minerals below them on the scale.1) Talc2) gypsum3) calcite4) fluorite5) apatite6) orthoclase7) quartz8) topaz9) corundum10) diamond The last three are not common minerals. Fingernail is 2 to 2.5, Cu penny is around 3.5; hammer is about 5.1, knife is 5.2 and plate glass is 5.5.SPECIFIC GRAVITYThis is the ratio of the density of the mineral to the density of water. It is obtained by weighing a piece of mineral in air and then in water. The difference in weight is equal to the volume of water displaced.Weight Air/(Weight Air-Weight in water) = specific gravitySpecific Gravity increases with increasing atomic weight of the cation. For example in the orthorhombic carbonates:Aragonite CaCO32.95Strontianite SrCO33.76Witherite BaCO34.29Cerrusite PbCO36.55Anhydrite CaSO42.98Celestite SrSO43.97Barite BaSO44.50Anglesite PbSO46.38COLOR AND STREAKColor is not a definitive property of a mineral, except when it is caused by a major constituent in the mineral. A good example of this is malachite that is green from the Cu. The mineral sphalerite (ZnS) can be yellow, black, red, green or varieties thereof. Quartz is usually colorless, however it can have many colors depending on trace amounts of cations that substitute in the structure. Streak: For opaque minerals, if you rub the sample across a streak plate, it will leave a colored powder. This streak is distinctive for minerals and is used to identify minerals. For example the mineral hematite can be brown, black, metallic grey and earthy. In all cases it give a red-brown streak. Play of Colors: Iridescence--For example, plagioclase  labradoriteInterference of light either at the surface or in the interior of a mineral--series of color--much the same as oil on water. Opal is another example.LUSTERMetallic or non-metallicNon-metallic: vitreous or glassy; silky; resinous; pearly; greasy; waxy,