18 Composition of minerals Atomic structureCentral region called the nucleusConsists of protons (+ charges) and neutrons (- charges)ElectronsNegatively charged particles that surround the nucleusLocated in discrete energy levels called shells
19 Composition of minerals Chemical bondingFormation of a compound by combining two or more elementsIonic bondingAtoms gain or lose outermost (valence) electrons to form ionsIonic compounds consist of an orderly arrangement of oppositely charged ions
30 Composition of minerals Isotopes and radioactive decayMass number = sum of neutrons + protons in an atomIsotope = atom that exhibits variation in its mass numberUnstable isotopes emit particles and energy in a process known as radioactive decay
31 Structure of mineralsMinerals consist of an orderly array of atoms chemically bonded to form a particular crystalline structureInternal atomic arrangement in ionic compounds is determined by ionic size
43 Physical properties of minerals ColorGenerally unreliable for mineral identificationOften highly variable due to slight changes in mineral chemistryExotic colorations of certain minerals produce gemstones
44 Quartz (SiO2) exhibits a variety of colors Figure 3.26
45 Physical properties of minerals StreakColor of a mineral in its powdered formHardnessResistance of a mineral to abrasion or scratchingAll minerals are compared to a standard scale called the Mohs scale of hardness
46 Streak is obtained on an unglazed porcelain plate Figure 3.12
48 Physical properties of minerals CleavageTendency to break along planes of weak bondingProduces flat, shiny surfacesDescribed by resulting geometric shapesNumber of planesAngles between adjacent planes
55 Physical properties of minerals Other propertiesMagnetismReaction to hydrochloric acidMalleabilityDouble refractionTasteSmellElasticity
56 Mineral groups Nearly 4000 minerals have been named Rock-forming mineralsCommon minerals that make up most of the rocks of Earth’s crustOnly a few dozen membersComposed mainly of the 8 elements that make up over 98% of the continental crust
57 Elemental abundances in continental crust Figure 3.18
58 Note:Oxygen is generally the only negative ion in silicatestructures. Some minerals (amphiboles, micas) formin a hydrated environment and contain an OH- ion.
59 Mineral groups Silicates Most important mineral group Comprise most rock-forming mineralsVery abundant due to large % of silicon and oxygen in Earth’s crustSilicon-oxygen tetrahedronFundamental building blockFour oxygen ions surrounding a much smaller silicon ion
60 Two illustrations of the Si–O tetrahedron Figure 3.19
61 Mineral groups Joining silicate structures Single tetrahedra are linked together to form various structures includingIsolated tetrahedraRing structuresSingle and double chain structuresSheet or layered structuresComplex 3-dimensional structures
63 Mineral groups Common silicate minerals Light silicates: Feldspar groupMost common mineral groupExhibit two directions of perfect cleavage at 90 degreesOrthoclase (potassium feldspar) and Plagioclase (sodium and calcium feldspar) are the two most common members
66 Mineral groups Common silicate minerals Light silicates: Quartz Only common silicate composed entirely of oxygen and siliconHard and resistant to weatheringConchoidal fractureOften forms hexagonal crystalsWhy is LI sand made mainly of quartz? Does it appear hexagonal?
67 Mineral groups Common silicate minerals Light silicates: Muscovite Common member of the mica familyExcellent cleavage in one directionProduces the “glimmering” brilliance often seen in beach sandMuscovite not often found inLI South Shore sand due towave and wind.Common in igneous granite rocksand metamorphic rocks
68 Mineral groups Common silicate minerals Light silicates: Clay minerals Clay is a general term used to describe a variety of complex mineralsClay minerals all have a sheet or layered structureMost originate as products of chemical weathering (often of feldspars)Note: “clay” can be a particle size for sediments. When used to describe a mineral, “clay” has a specific formula and structure.
69 Mineral groups Common silicate minerals Dark silicates: Olivine group High temperature Fe-Mg silicatesIndividual tetrahedra linked together by iron and magnesium ionsForms small, rounded crystals with no cleavageFe2SiO4 and Mg2SiO4
70 Mineral groups Common silicate minerals Dark silicates: Pyroxene group Single chain structures involving iron and magnesiumTwo distinctive cleavages at nearly 90 degreesAugite is the most common mineral in the pyroxene group
71 Mineral groups Common silicate minerals Dark silicates: Amphibole groupDouble chain structures involving a variety of ionsTwo perfect cleavages exhibiting angles of 124 and 56 degreesHornblende is the most common mineral in the amphibole group
79 Mineral groups Important nonsilicate minerals Carbonates Primary constituents in limestone and dolostoneCalcite (CaCO3) and dolomite CaMg(CO3)2 are the two most important carbonate minerals
80 Mineral groups Important nonsilicate minerals Many nonsilicate minerals have economic valueExamplesHematite (oxide mined for iron ore)Halite (halide mined for salt)Sphalerite (sulfide mined for zinc ore)Native copper (native element mined for copper)
81 Native copper is a native element. What are some other native elements?
82 What are some other native elements? GoldPlatinumCopperSilverSulfurDiamondGraphite
83 Minerals are considered gemstones if the cost of producing the gem is less than the market value.
85 Gemologist A gemologist uses diagnostic tests to identify minerals Sophisticated equipment can detect mineral type, artificial color enhancement, and drilled or filled flawsDo you know the meaning of karat? Carat? Caret? Carrot?