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Primary Characteristics of Minerals 1) Crystal Shape if grown unimpeded, minerals will have a consistent shape specific to that mineral often confused with cleavage crystal shape is the original shape of the mineral very useful if present 2) Lustre the reflective nature of the mineral's surface split into two broad categories, metallic or non-metallic non-metallic can be further broken down to glassy, pearly, silky, resinous, earthy or dull these descriptions are somewhat subjective often a starting point for classification 3) Colour a relatively useless characteristic some minerals do have distinct colours, but there are two problems many minerals have similar colours some minerals have a variety of colours Quartz Given the samples of quartz shown, why might the following properties not be useful? Crystal shape Lustre Colour 4) Streak colour in a powdered form the "true colour" of the mineral obtained by rubbing a mineral off of a streak (porcelain) plate while quartz may be many different colours, the streak is always white 5) Hardness the ability to resist scratching has to do with the strength of bonds within the minerals a harder mineral is capable of scratching a softer mineral Moh's Hardness Scale a series of benchmark minerals ranked from 1 - 10 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. Ex) An unknown mineral can scratch apatite and can be scratched by a steel screwdriver. What might its hardness be? Ex 2) There are 3 minerals (A, B, and C) "A" can cut glass "B" can cut "A" "C" can be scratched by fingernails Rank them from softest to hardest Ex 3) Sort the given list into the following catergories. Can Cut Glass Can Be Scratched by Finger Nails 6) Cleavage / Fracture the way that minerals tend to break cleavage - breaks along planes fracture - breaks unevenly cleavage can be described by: the number of planes angle that the planes meet for example: How would we describe the cleavage of calcite? not all cleavage is perfect, but the patterns should be regular enough to spot if the mineral breaks in an irregular manner, it fractures fracture can be broken up in several categories, but we limit it to either conchoidal: nonconchoidal: 7) Specific Gravity similar to density a number that compares the mass of a mineral to the amount of water it displaces if a mineral displaces 3 times more water than its mass, then it has a specific gravity of 3 if the mineral has a low specific gravity it will feel "too light" a high specific gravity feels "too heavy" Describe the specific gravity of hematite versus gypsum. Calculating Specific Gravity a cubic centimetre (one millilitre) of water has a mass of approximately one gram by comparing the mass of the rock to the amount of water displaced, we can calculate the specific gravity Ex) How much water is displaced by the by the rock? Ex 2) If the rock has a mass of 150 g, what is the specific gravity of the rock? Secondary Properties extremely useful when present, but not common enough to start with 1) Taste some minerals have a distinct taste for example halite tastes salty can be unsafe with some minerals 2) Smell a few minerals have a distinct smell for example, sulfur smells like rotten eggs 3) Magnetism some minerals are ferromagnetic meaning that they are attracted to magnets for example, magnetite some minerals are only slightly magnetic and difficult to notice 4) Fluorescence some minerals glow under UV light (blacklight) for example, fluorite has a greenish glow 5) Acid reaction carbonate minerals bubble in the present of acid for example, calcite 6) Optical Properties some minerals cause light to bend in strange ways that can be observed for example, calcite displays double refraction Commonly Confused Minerals often minerals that look the same can be confused for each other this is why pyrite is known as fool's gold (it is similar in appearance to gold) it is important to know some quick ways to tell these common minerals apart Ex 1) Pyrite and Gold Pyrite lustre: metallic color: brass yellow streak: greenish-black hardness: 6 specific gravity: 5.2 Gold: lustre: metallic color: rich yellow streak: rich yellow hardness: 2.5 - 3 specific gravity: 19 Ex 2) Barite and Quartz Barite lustre: color: streak: hardness: specific gravity: cleavage: Quartz lustre: color: streak: hardness: specific gravity: fracture: Ex 3) Halite and Calcite Ex 4) Calcite and Quartz Ex 5) Talc and Gypsum