Minerals, Plummer Chapter 2 What is a mineral? Silicate minerals GemstonesMarch 1, 2004Exams- so far so good! Exams will be returned anddiscussed after all make-ups are completed. Test your diamond-buying skills

What is a mineral? The traditional definition Naturally occurring substance Solid InorganicNOTE: many minerals are produced by BOTH inorganic ANDbiological processes (biomineralization). Calcite - shells of marine organismsMagnetite- bacteriaApatite- bones and teeth Has a set of physical properties that are the same for any andall samples of a given mineral.

Mineral or Not a MineralHalite, NaCl ?

Mineral or Not a MineralLiquid H2O ?Ice, H2O ?

Mineral or Not a MineralAmber (C10H16O) ?

Mineral or Not a MineralPearls?

Crystal Structure is usually the sticking point for mineral/not a mineralCrystallinity- a regularly repeating patternLinear pattern (1-dimensional)

2 dimensional patternMap ViewWhat do I get if I stack this 2-D pattern one on top of the otherfrom the floor up to the ceiling?What do I get if I put several chains side by side on the floor?

Plummer et al., Physical Geology 9th edition, McGraw Hill Inc, Fig 2.023-dimensional patternConnect the centers of the blue circles- cubic structure

Plummer et al., Physical Geology 9th edition, McGraw Hill Inc, Fig 2.02NaCl - table saltSodium (Na)Chlorine (Cl)NaCl held together by ionic bond, which is easy to break --> cleavageand hardness

A (paraphrased) question from Super MillionaireWhat is the most abundant element in the Earths crust?8 elements make up98.6 % of the Earths crust.ElementsymbolOxygenSiliconAluminumIronCalciumSodiumPotassiumMagnesiumOSiAlFeCaNaKMgThe building blocks of minerals

Main rock-forming mineral groups Silicates Oxides building block is SiO4 tetrahedron make up the majority of crustal rocks composed on metal + oxygenCarbonates important component of sedimentary rocks building block is CO3 ion

SiO44- complex ion A group of ions that is so tightly bound together that they act like a single unit. Building block of silicate minerals 1 silicon ion + 4 oxygen ions arranged in a triangular pyramid Electrical charge of -4

Plummer et al., Physical Geology 9th edition, McGraw Hill Inc, Fig 2.07

Silicate tetrahedronSiO44-

Tetrahedron ViewingView from the top,looking down.Top point oftetrahedronfacing youFlat base of tetrahedronfacing you. Top pointof tetrahedron pointingaway from you.

Nesosilicates (island silicates)SiO44- tetrahedron forms ionic bonds with cations such as Mg2+, Fe2+Fe2SiO4 - FayaliteMg2SiO4 - Fosterite(Mg, Fe)SiO4Solid solutionExample: Olivine

Olivine: nesosilicate structure (island silicate)Why Mg OR Fe? Same size Same electricalcharge

Corner Sharing Base to Baseside view3-D Side View

Inosilicicates: Single Chains (Pyroxene)SiO3 Chain forms ionic bonds with cations above the tipand below the base 2 Si6 OPlummer et al., Physical Geology 9th edition, McGraw Hill Inc, Fig 2.11

Corner Sharing Tip to TipExtra slide. Not shown in class. Not for exams. For your interest.Face sharing

Extra slide. Not shown in class. Not for exams. For your interest.Assembling a Single Chain Silicate (Pyroxene)

Extra slide. Not shown in class. Not for exams. For your interest.Pyroxene- Wheres the cleavage?90 cleavage

Extra slide. Not shown in class. Not for exams. For your interest.This wont work.No gold, silver, or uraniumfound with pyroxens.

Double Chain Silicates (Amphibole)PAIR of SiO4 chains that link by corner sharing in 2 directions Plummer et al., Physical Geology 9th edition, McGraw Hill Inc, Fig 2.11

Plummer et al., Physical Geology 9th edition, McGraw Hill Inc, Fig 2.11Amphibole formula is long: lots of space for smalland medium cationsCations include Na+, K+, Ca2+, Mn2+,Fe2+, Mg2+, Fe3+, Al3+, Ti4+ Extra slide. Not shown in class. Not for exams. For your interest.

Extra slide. Not shown in class. Not for exams. For your interest.60-120 Cleavage in Double Chain Silicates (Amphibole)- (actually 56 - 124)breaking at the molecular scaleWhat human eyes seeat the macro scale

What is Jade?Both pryoxeneAND amphiboleare Jade.Other JadesAfrican jade: Green garnetAmazon jade: Green K-feldsparIndian jade: Green quartzJadeite = NaAlSi2O6Nephrite = Ca2(Mg,Fe)5Si8O22(OH)2

Plummer et al., Physical Geology 9th edition, McGraw Hill Inc, Box 02.03.f1, photo by C.C. PlummerAsbestos- generic name for fibrous amphibole

Ring Silicates- BerylStack of SiO4 rings, builtup out of the plane of screen

Plummer et al., Physical Geology 9th edition, McGraw Hill Inc, Fig. 2.14Muscovite

Clay minerals: talc, kaolinite, illite, chlorite, montmorilloniteYou know them better as: baby powder, kaopectate/non-dairy creamer,facial mask, soapstone, and kitty litter.Main difference- ions that make up the middle of the sandwich

Quartz No cleavage. Covalent bondsare equally strong in all directions very roomy structure. Can accommodate large cations.

Gold, silver always found with quartz Hardness of 7 on Mohs scale,also due to crystal structure. All oxygens are shared

Gemstones- beautiful, rare, durableWhat makes a mineral a gem?Fluorite- gem or not a gem?

GarnetRubyAmethystAquamarineDiamondEmeraldPearlPeridotSapphireOpalTopazTurquoiseBirthstones- Gem names

GarnetCorrundumQuartzBerylDiamondBerylPearlOlivineCorrundumAmorphousquartzAl-F silicateHydrouscopper phosphateBirthstones- The real names!

Ruby and Sapphire- forms of Corundum Al2O3Ruby- corundum with chromiumSapphire- corundum with iron and titanium

A quick guide to buying diamonds- Color Cut Clarity Carat

Gem- rare, beautiful, durableA typical diamond deposit yields ~ 5 grams of diamondper 1000 kg of rock mined.

1. Color- Which one is the most valuable?ColorlessNearcolorlessFaint yellowVery LightyellowLightyellowFancyyellow

The Hope DiamondPossibly the re-cut (4 times) Tavernier Blue Diamond,which was reported at 112 carats in the year 1668. 45 carats

2. CutTableCrownMain pavillion

Cutting DiamondsMarshak, S. Earth, Portrait of a Planet, W.W. Norton, Fig. 5.26

Why are diamonds cut this way?Facets control the pat of light traveling through the diamond.The more light that exits the top (crown), the more it sparkles.Pat of light in a round brilliant diamond

Imperfections in the cut

3. ClarityAre there blemishes on the surface, or inclusions insidethe diamond?

4. Carat weight1 carat (ct.) = 200 milligramsBig diamonds are more rare than little diamonds.

A 2 ct diamond costs more than 2 times a 1 ct. diamond.Note: carat weight NOT THE SAME as gold karats. Gold is made of 24 parts.Karats indicates how many of those 24 parts are gold.14 karat gold = 14 parts gold + 10 parts alloying metal (copper, nickel, silver)18 karat gold = 18 parts gold + 6 parts alloying metal.

Is my diamond a fake?!Zirconium Oxide (ZrO2)Cubic ZirconiaSilicon Carbide (SiC)MoissaniteExtra credit for exam 2:How can you tell the difference betweena real diamond and one of these substitutesUsing physical properties?Note- you will not be allowed to leave the room during exam 2 to consult an appraiser.