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  • What is a mineral?

  • A mineral is the basic building blocks all rocks.

  • Different mineral mixes reveal the rocks origin and give the rock its name.

  • Geologists and Mineralogist, who are scientists who study

  • minerals and mineral formation, have identified and named

  • over 6,000 different minerals.

  • Minerals come in a rainbow of different colors and crystal structures.

  • A mineral must meet five qualities to be considered a mineral.

  • A mineral is solid.

  • A mineral is naturally occurring.

  • That means it's never man-made

  • A mineral has an inorganic origin.

  • that means that the mineral comes

  • from non-living things.

  • A mineral has a crystal structure.

  • The atoms that make it up have a regular repeating pattern.

  • A mineral has a definite chemical formula.

  • The atoms that make it up will always be the same

  • Silica will always be SiO2

  • and calcite will always be CaCO3

  • Rocks are made-up of minerals.

  • Minerals are not rocks.

  • The most valuable minerals tend to be metal ores,

  • or minerals that we can extract metals from.

  • Many minerals contained metallic elements which can be extracted

  • which can be extracted

  • Other minerals are useful for their chemical compounds in flavoring our food

  • Salt is a prime example it comes from mineral halite.

  • graphite is using a number of products including

  • the core of pencils.

  • Still other minerals are prized for their beauty and elegance

  • Gemstones and jewelry are just a few of these treasures.

  • Due to the huge number of minerals in the world

  • Geologists use several different tests to determine

  • the identity as a mineral.

  • The first and most basic is color

  • The problem with color

  • is that small impurities within the crystal structure

  • can dramatically change the appearance of a mineral.

  • In addition several minerals may share the same color.

  • Green is a very common color among minerals which contained copper.

  • A small amount of titanium can change colorless diamond blue.

  • The next test which can be performed

  • is density.

  • Density is a measurement

  • of the ratio of a minerals mass to its volume.

  • The more mass contained in a given volume

  • the greater the density.

  • We calculate density

  • as a ratio of mass to volume.

  • First we measure the mass a mineral sample using a balance.

  • Because mineral samples are usually

  • unevenly shaped, we can use the water displacement method to determine the

  • volume of the sample.

  • The graduated cylinder here has three hundred milliliters of water in it.

  • When we add the mineral sample to the cylinder,

  • it now reads 375 milliliters.

  • The seventy five milliliter increase is the volume

  • the sample took up.

  • Density can then be calculated

  • by dividing the mass by the volume.

  • Crystal structure is a repeating geometric configuration

  • having straight edges and flat faces.

  • The atoms within a mineral are arranged

  • in an ordered repeating way.

  • Crystals can be very small

  • and not always visible to the human eye.

  • But all minerals

  • will have a crystal structure.

  • An eerie calm rolls

  • across some barren stretch of land.

  • but deep within the earth something strange

  • and beautiful is happening.

  • Within moments, rumblings from below break the silence.

  • And in a tremendous explosion of

  • fire and heat

  • molten lava spews forth

  • in all directions,

  • bearing witness to the fury below.

  • Within the earth's molten liquid rock,

  • Minute particles called atoms

  • dance wildly in every direction.

  • As this molten mass cools,

  • the movement of atoms slows down,

  • and similar atoms begin

  • bonding themselves together in an orderly fashion.

  • This process is called crystallization.

  • Which results in the formation of solid minerals.

  • If conditions are just right, atoms of the same minerals and will continue to

  • bond together

  • creating wondrous crystal shapes.

  • These crystal forms represent an outward expression

  • of the internal arrangement of atoms.

  • But what happens when two or more minerals of different types.

  • crystallized together?

  • We'd have the birth

  • of a common rock

  • The shape and structure at the Crystal reflects the pattern

  • or arrangement atoms and molecules found within the mineral.

  • Crystals are divided into six patterns. Ranging from simple cubic

  • shapes, to complex multi-sided shapes.

  • Depending on how the atoms within a crystal are arranged, a mineral can have

  • very different hardness properties.

  • Hardness is the scratchability of a mineral.

  • We use the Moh's hardness scale of minerals

  • to give a numeric value to the hardness of a mineral.

  • The Moh's scale uses a set of 10 common index minerals

  • ranging from talc, used in baby and body powder, at 1

  • to diamonds, the world's hardest known material, at 10.

  • We use this set have known materials to scratch an unknown sample

  • and then compare the results against the Moh's hardness scale.

  • Index mineral 1 does not scratch the sample.

  • The sample is harder than a 1.

  • Index mineral 2 does not scratch the sample

  • So the sample is harder than a 2.

  • Index minerals 3 does not scratch the sample.

  • So the sample is harder than a 3. index mineral for

  • Index mineral 4 does not scratch the sample.

  • The sample is harder than a 4.

  • Index mineral 5 does not scratch the sample.

  • The sample is harder than a 5.

  • Index mineral 6 does not scratch the sample.

  • So the sample is harder than a 6.

  • Index mineral 7 does scratch the sample.

  • See the little scratch?

  • That means that the mineral sample is softer than a 7.

  • Halfway between 6 and 7 is 6.5

  • The mineral has a hardness of 6.5.

  • The next test to consider is luster.

  • Luster is how light reflects off a crystal face.

  • Luster is divided into two categories

  • either metallic or non-metallic.

  • Metallic lusters look like metal non-metallic lester's

  • Non metallic lusters do not.

  • Luster- the way light is reflected from the mineral's surface.

  • Waxy, Metallic

  • earthy, and vitreous are all words used to describe luster.

  • Because color can be unreliable,

  • scientists use a streak test to determine the true color of a mineral.

  • Minerals can react with the atmosphere and appear very different to their true color

  • The streak is the color of the powdered mineral.

  • Streak is usually found by rubbing a mineral sample

  • against a piece unglazed porcelain.

  • Minerals harder than the streak plate,

  • which has a hardness of 7, will not have a streak

  • because the plate is not hard enough to grind up the mineral sample.

  • When a mineral breaks it can break in one of two ways:

  • it can cleave or it can fracture.

  • Cleavage is a tendency is a mineral to break along flat plains and straight lines

  • A mineral may have cleavage in only one direction,

  • such as mica, which breaks off into thin sheets.

  • There can be two directions of cleavage.

  • Creating breaks that have two flat surfaces and one jagged surface.

  • This is a way that feldspars break.

  • Lastly, you can have three planes of cleavage,

  • creating cubes or rhombahedrons.

  • Galena and Halite

  • both have three planes of cleavage

  • and break into small cubes when broken.

  • Look at this mineral sample.

  • When broken with a hammer, small flat pieces up the sample flake off.

  • Because these pieces have flat plains and surfaces

  • the mineral shows cleavage when broken.

  • If a mineral does not have cleavage, it has fracture.

  • Fracture occurs when a mental breaks

  • in an uneven or rough way.

  • Quartz does not cleave, instead it fractures with a rough and uneven edge.

  • This specific type of fracture shown by quartz is called concoidal fracture.

  • fracture

  • Look at this mineral sample.

  • When broken with a hammer

  • uneven and irregular pieces are broken off.

  • These pieces have no flat plains or surfaces.

  • instead they're completely irregular.

  • This mineral shows fracture, not cleavage.

  • There are several other tests that can help identify a mineral.

  • Some minerals such as fluorite and some samples of calcite

  • will fluoresce under ultraviolet light.

  • Magnetite an iron ore is magnetic, hence its name

  • Sulfur has a particularly pungent smell and is recognizable

  • as the smell of matches as well as brimstone.

  • Many carbonate minerals react to acid by creating carbon dioxide

  • which fizzes and effervescences on the surface.

  • Halite, or sodium chloride NaCl,

  • taste like salt, because it is salt.

  • However it's not a good idea to lick minerals,

  • the sample could have been in contact with many hands

  • and you wouldn't wanna lick all those people.

What is a mineral?

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B2 中高級 美國腔

鑑定礦物的測試 (Tests to Identify Minerals)

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    leo 發佈於 2021 年 01 月 14 日
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