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Oyster / muscle shellsTeeth CrystaloSingle, continuous, piece of crystalline solidoBound by flat surfaces (crystal faces) with regular geometric form occurring naturallyoConsistency of interfacial anglesoThe same mineral has the same crystal faces and angles between themoCrystal examples:oDiamond, quartz, garnet, etc.oCrystals interact with light to create attractive beautyoX-Ray Diffraction (XRD) proposed by Max van Laueis still used to look inside crystalsoThe order of the atoms in a crystal repeat regularly in three dimensionsoThis is called Crystal LatticeoThe order of these atoms display symmetry, and this order defines the crystal structureoPhysical properties of crystal depend on:oIdentity of atomsoArrangement of atomsoNature of atomic bondsoDiamondand graphiteare made entirely of CarbonoDiamond- atoms are arranged in tetrahedral (hardest mineral)oGraphite– atoms arranged in sheets; softest mineraloPolymorph– same composition, different structureMineral FormationoNew crystals form in 5 different ways:oSolidification from a meltoCrystals grow when the melt coolsoLiquid freezes to form solidoPrecipitation from solutionoSeeds form when precipitation becomes saturated
oSolid State diffusionoGarnetsoBiomineralizationoOur tooth enamel is mineral apatiteoPrecipitating from GasoTiny early crystal acts as seed for growthoAtoms migrate to seed and attachoGrowth moves face outward from centeroSometimes if crystals grow in confined spaces, they don’t have faces, as the faces are obstructed by objects around the crystaloAnhedral– grown in tight space, no facesoEuhedral– grown in open cavity, good facesMineral DestructionoMinerals can be destroyed by:oMelting – heat breaks the bonds holding atoms togetheroDissolving – solvents break atomic bondsoChemical reaction – reactive materials break bondsMineral Physical Properties:oColoroStreakoColor of powder produced from crushing a mineraloLusteroThe way mineral surface scatters light, metallic, or non-metallicoHardnessoScratching resistanceoDerives from strength of atomic bondsoSpecific gravityoDensity of mineraloHow heavy it feelsoCrystal habitoShape characteristicsoIs it a single crystal with well-formed faces, an aggregate of many well-formed crystalsoRecords variation in directional growthBlock = same speed growth in all directionsNeedle-like = fast growth in only one directionoFracture or cleavageoMinerals break in ways that reflect their atomic bondsoFracturing implies equal bond strength in all directions oCleavage – tendancy to break along planes of weaker atomic bondsProduces flat, shiny surfacesCleavage is all through the crystal, usually produces parallel steps, where crystal faces only occuron external facesMineral ClassificationoMinerals can be broken into a few groups. J. J. Berzelius, a Swedish chemist, noted similaritiesoMinerals can be separated by:o