Minerals Definition, Types, and Identification Department ...

1 MineralsDefinition, Types, and IdentificationForensic ApplicationsDepartment Environmental, Earth, & Atmospheric SciencesTransparent emerald, the green variety of beryl, on calcite matrix Niocalite (blue) in sovite (calcite + apatite). Oka carbonatite complex. Crossed-polars. Width = mm Department Environmental, Earth, & Atmospheric SciencesMineralsMinerals Building blocks of rocks, soil ,dirt, and mudBuilding blocks of rocks, soil ,dirt, and mud Minerals are everywhereMinerals are everywhere Rocks are aggregates of one or more mineralsRocks are aggregates of one or more mineralsFluoriteGneissDepartment Environmental, Earth, & Atmospheric SciencesMineral DefinitionMineral OccurringNaturally Crystalline has a definite internal structure, has a definite internal structure.

2 Atoms in the mineral are arranged in a , atoms in the mineral are arranged in a regular wayregular composition fixed or varies within Chemical composition fixed or varies within certain limitscertain limitsDepartment Environmental, Earth, & Atmospheric SciencesMineralsMinerals Naturally OccurringNaturally Occurring-- Minerals must be formed Minerals must be formed naturally naturally --glass, concrete, synthetic diamonds, glass, concrete, synthetic diamonds, rubies and emeralds donrubies and emeralds don t countt count InorganicInorganic-- Minerals are not formed by anything Minerals are not formed by anything that was ever alive.

3 Therefore, materials such that was ever alive. Therefore, materials such as: Ivory, Amber, Coal, Pearlsas: Ivory, Amber, Coal, Pearlsare not Minerals !are not Minerals ! Department Environmental, Earth, & Atmospheric SciencesMineralsMinerals CrystallineCrystalline--the atoms in Minerals have an the atoms in Minerals have an orderly atomic arrangement giving them a orderly atomic arrangement giving them a definite structure that controls their structure that controls their Environmental, Earth, & Atmospheric SciencesMineralsMinerals ChemistryChemistry--Chemical composition is fixed or Chemical composition is fixed or varies within certain limits.

4 Crystalline varies within certain limits. Crystalline compounds with the same structure but compounds with the same structure but different chemistry form different chemistry form different array of atomsNaCl = HaliteKCl = SylviteDepartment Environmental, Earth, & Atmospheric SciencesIons are arranged in crystal structures according to their relative sizes. This is referred to as closest packing. We usually look at this from the perspective of the cation and calculate the radius ratio = size cation/size anion. The radius ratio determines the number of anions that can be packed around a particular of MineralsCrystal Lattice: the three dimensional molecular structure of a mineral.

5 (Shape of the unit cell. ) Various ions make up the mineral. Geometry + chemistry!Structure of MineralsDepartment Environmental, Earth, & Atmospheric SciencesStructure of mineralsStructure of mineralsPolymorphsPolymorphs Minerals with the same composition but different crystalline Minerals with the same composition but different crystalline structuresstructures Examples include diamond and graphiteExamples include diamond and graphite Phase change Phase change one polymorph changing into anotherone polymorph changing into anotherDiamondGraphiteDepartment Environmental, Earth.

6 & Atmospheric SciencesPhysical properties of mineralsPhysical properties of mineralsCrystal FormCrystal Form External expression of a mineralExternal expression of a mineral s internal s internal structurestructure Often interrupted due to competition for space and Often interrupted due to competition for space and rapid loss of heatrapid loss of heatCrystals are the smallest Crystals are the smallest bitsbits of Minerals of Minerals and reflect the geometry of the mineral and reflect the geometry of the mineral moleculesmoleculesDepartment Environmental, Earth.

7 & Atmospheric SciencesPhysical properties of mineralsPhysical properties of mineralsColorColor Generally unreliable for mineral identificationGenerally unreliable for mineral Identification Often highly variable due to slight changes in Often highly variable due to slight changes in mineral chemistrymineral chemistry Exotic colorations of certain Minerals produce Exotic colorations of certain Minerals produce gemstonesgemstones Some Minerals are used as pigmentsSome Minerals are used as pigmentsDepartment Environmental, Earth, & Atmospheric SciencesQuartz (SiO2) Quartz (SiO2)

8 Exhibits a variety exhibits a variety of colorsof colorsPhysical properties of mineralsPhysical properties of mineralsStreakStreakColor of a mineral in its powdered formColor of a mineral in its powdered formDepartment Environmental, Earth, & Atmospheric SciencesStreak is Streak is obtained on an obtained on an unglazed unglazed porcelain plateporcelain platePhysical properties of mineralsPhysical properties of mineralsLusterLuster Appearance of a mineral in reflected lightAppearance of a mineral in reflected light Two basic categoriesTwo basic categories MetallicMetallic NonmetallicNonmetallic Other descriptive terms include vitreous, Other descriptive terms include vitreous, silky, or earthysilky, or earthyDepartment Environmental, Earth.

9 & Atmospheric SciencesGalena (Galena (PbSPbS) displays ) displays metallic lustermetallic lusterPhysical properties of mineralsPhysical properties of mineralsHardnessHardness The hardness of a The hardness of a mineral is its mineral is its resistance to resistance to The standard The standard scale for scale for measuring measuring hardness is hardness is MohMoh ssHardness Environmental, Earth, & Atmospheric SciencesPhysical properties of mineralsPhysical properties of mineralsCleavageCleavage Tendency to break along planes of weak Tendency to break along planes of weak bondingbonding Produces flat, shiny surfacesProduces flat, shiny surfaces Described by resulting geometric shapesDescribed by resulting geometric shapes Number of planesNumber of planes Angles between adjacent planesAngles between adjacent planesDepartment Environmental, Earth, & Atmospheric SciencesFluorite, halite, and Fluorite, halite.

10 And calcite all exhibit calcite all exhibit perfect cleavageperfect cleavageCleavageCleavageDue to planes of weakness caused by alignment Due to planes of weakness caused by alignment of the common crystal facesof the common crystal facesDepartment Environmental, Earth, & Atmospheric SciencesDepartment Environmental, Earth, & Atmospheric SciencesPhysical properties of mineralsPhysical properties of mineralsFractureFracture Absence of cleavage when a mineral is brokenAbsence of cleavage when a mineral is brokenSpecific GravitySpecific Gravity Weight of a mineral / weight of an equal volume Weight of a mineral / weight of an equal volume of waterof water Average value = value = Environmental, Earth.