physical science 120 physical properties of minerals

PHYSICAL SCIENCE 120PHYSICAL PROPERTIES OF

MINERALS

As you view the PHS 120 Power Points you will be prompted to advance to the next slide when you see this symbol (*).

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Mineral Definition……………….……Slide 3Hardness……………………………………..8Cleavage……………………………….…...12Fracture……………………………..…..….19Streak………………………………………21Luster…………………………..……….….23Color……………………………………….28Specific Gravity…………………………....31Taste……………………………………….48Magnetism…………………………………49Double Refraction…………………………53Reaction to HCl (acid)…………………….54Diaphaneity………………………………..56Crystals………………………………….…60 Isometric……………………………….…..62Hexagonal……………………………….…66Tetragonal………………………………….70Orthorhombic…………………………..…..74Monoclinic………………………………....79Triclinic…………………………………….82Resources…………………………………..85

TABLE OF CONTENTS

This list of slides will allow you to review the various topics of the presentation. (*)

During the presentation you can “right mouse click” on a slide to go to the edit mode. (*)

Physical Science 120 students are required to do pages 1 – 54.

Mineral Identification Basics• What is a Mineral?

There is a classic four part definition for mineral.

Minerals must be: (*) Naturally occurring (*)

Inorganic (*)

Possess a definite crystalline structure (*)

Have a definite chemical composition (*)

Cubic Fluorite Crystal


Minerals are not synthetic - they are produced by the natural geological processes working on Earth. For example, steel, brass, bronze and aluminum are not considered minerals in that they are not found in nature. (*)

Technically speaking, synthetic gemstones are not considered minerals. This area of mineralogy has a hazy boundary in that synthetic stones are in every way the same as the natural stones. But because they are produced in laboratories, they do not meet the classic definition of a mineral. (*)

Also note that many synthetic gemstones are “doped” with a fluorescent dye to distinguish them from natural stone. (*)

Tourmaline Crystal from Brazil

Naturally Occurring (*)


Minerals are NOT produced by organic processes. As a result things like pearls, coral, coal and amber are not considered minerals.

Also included in this

“NOT a Mineral List” are teeth, bones, sea shells and

even kidney stones. (*)Barite Rose - A flower like growth

of Barite crystals.

Inorganic (*)


Minerals are the result of atoms joining together through electrical bonds to produce a definite internal structure. (*)

Crystalline Pattern of Halite

Red = Sodium

Green = Chlorine

Internal Structure

Halite (salt) from Searles Lake, CA

It is the nature of the atoms and the strength of the chemical bonds that determine many of the minerals’ physical and chemical properties. (*)

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Minerals can be expressed by a chemical formula. The internal order of minerals means that there is a definite relationship in the number of atoms that makes up the mineral. (*)

Halite - NaCl

For every atom of Sodium there is an atom of Chlorine.

Definite Chemical Composition (*)

Mineral Identification Basics• PHYSICAL PROPERTIES HARDNESS

HARDNESS is defined as the resistance a mineral has to being scratched - its “scratchability”. Hardness tests are done by scratching one mineral against another. The mineral that is scratched is softer than the other. (*)

Pyrite Crystals

Hardness of 6.5 (*)


In this photo, a quartz crystal will be rubbed across a glass plate. The result is that the glass plate will be scratched. The quartz is therefore harder than the glass. (*)

Quartz is harder than glass.

HINT: In doing a hardness test try to pick a smooth or flat surface on the mineral to be scratched. Try to pick a point or a sharp edge on the mineral that you think will do the scratching. Glass is usually a good place to start because it is in the middle of the hardness table, it has a flat, smooth surface and it is easily obtained. (*)


Care must be taken on some minerals that crumble easily. Remember that hardness is the resistance a mineral has to being scratched - NOT how easily it breaks apart. The physical property related to the ease in which a mineral breaks is tenacity. (*)

Also be sure to determine the hardness of a mineral on a fresh surface whenever possible. Some minerals have a tendency to oxidize or corrode. These surface deposits usually have a different hardness than the fresh mineral. (*)

Moh’s scale is a list of minerals with increasing hardness.(*)


MOH’S SCALE OF MINERAL HARDNESS

1. TALC

2. GYPSUM

3. CALCITE

4. FLUORITE

5. APATITE (*)

6. FELDSPAR

7. QUARTZ

8. TOPAZ

9. CORUNDUM

10. DIAMOND (*)

OTHER MATERIALS COMMONLY USEDOTHER MATERIALS COMMONLY USED::

2.5 - FINGERNAIL2.5 - FINGERNAIL 3 - COPPER PENNY 3 - COPPER PENNY

5.5 - GLASS 6-6.5 - STEEL FILE5.5 - GLASS 6-6.5 - STEEL FILE(*)

Mineral Identification Basics• PHYSICAL PROPERTIES CLEAVAGE

CLEAVAGE is the property of a mineral that allows it to break repeatedly along smooth, flat surfaces. (*)

These GALENA cleavage fragments were produced when the crystal was hit with a hammer. Note the consistency of the 90o angles along the edges. (*) These are FLUORITE cleavage

fragments. (*)


Within this crystalline pattern it is easy to see how atoms will separate to produce cleavage with cubic (90o) angles. (*)

It is similar to tearing a piece of paper that has perforations in it. The paper has a tendency to tear along the perforations. They are zones of weakness. (*)

In this example the lines represent breaks between the atoms that make up the mineral. Cleavage is guided by the atomic structure. (*)


These pictures show different cleavage angles and the quality of cleavage.

Fluorite has cleavage in four directions. (*)

A thin sheet of Muscovite seen on edge.

Mica has perfect cleavage in ONE direction. (*)


Common salt (the mineral HALITE) has very good cleavage in 3 directions. (*)

These 3 directions of cleavage are mutually perpendicular resulting in

cubic cleavage. (*)


Rhombohedral Cleavage - 3 directions

CALCITEEven these tiny fragments have rhombohedral cleavage. (*)

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Blocky Cleavage 2 directions

Orthoclase Feldspar (*)

Orthoclase feldspar has good cleavage in 2 directions.

The blocky appearance of this specimen is a hint that it has cleavage. The clue that the specimen has cleavage is the fact that numerous faces will reflect light at the same time. Each face is parallel and light will reflect of each face producing a flash of light. (*)

Note that the faces in the circle are at different levels. By adjusting the lighting, all of the parallel faces will reflect simultaneously. This results in a flash of light from all the parallel faces. (*)


TALC has micaceous cleavage. That is to say that it cleaves like mica (1 perfect direction) but, in talc the crystals are so small that they cannot easily be seen. Instead the effect is that the talc “feels soapy”. The second picture shows some of the talc that has cleaved onto the fingers. (*)

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Mineral Identification Basics• PHYSICAL PROPERTIES FRACTURE

FRACTURE is defined as the way a mineral breaks other than cleavage. (*)

This is a piece of volcanic glass called OBSIDIAN. Even though it is NOT a mineral, it is shown here because it has excellent conchoidal fracture. (*)

If you try this yourself, use caution. Conchoidal fracture in obsidian can produce extremely sharp edges. (*)

Mineral Identification Basics• PHYSICAL PROPERTIES FRACTURE

This Quartz crystal will be struck with a hammer to show how that the external form of the crystal does not repeat when broken. (The flat crystal faces are not cleavage faces.)

This is a good example of conchoidal fracture. (*)

Note the smooth curved surfaces. (*)

Mineral Identification Basics• PHYSICAL PROPERTIES STREAK

STREAK is defined as the color of the mineral in powder form. (*)

Hematite on Streak Plate

Streak is normally obtained by rubbing a mineral across a “streak plate”. This is a piece of unglazed porcelain. The streak plate has a hardness of around 7 and rough texture that allows the minerals to be abraded to a powder. This powder is the streak. (*)

Hematite has a reddish brown streak. (*)

Mineral Identification Basics• PHYSICAL PROPERTIES STREAK

Sphalerite is a dark mineral, however, it has a light colored streak. Next to the reddish brown streak of hematite is a light yellow streak. This is the streak of the sphalerite. (*)

Sphalerite has a light yellow streak. (*)

Light colored streaks are often difficult to see against the white streak plate. It is often useful to rub your finger across the powder to see the streak color. (*)

Mineral Identification Basics• PHYSICAL PROPERTIES LUSTER

LUSTER is defined as the quality of reflected light. Minerals have been grossly separated into either METALLIC or NON-METALLIC lusters.

Following are some examples: (*)

Native Silver has a Metallic Luster. (*)

The basic idea for Metallic Luster is that the minerals look like metals. (*)

Mineral Identification Basics• PHYSICAL PROPERTIES LUSTER METALLICLUSTER METALLIC

Stibnite Galena

Marcasite Pyrite (*)

Vitreous Luster means that the mineral has a “glassy” look. Normally we think of glass as being clear, but there are many different colors of glass and they are all very “glassy” looking. Even china plates and glazed porcelain are vitreous. Here are some examples: (*)

Mineral Identification Basics• NON-METALLICNON-METALLIC LUSTER VITREOUSLUSTER VITREOUS

Olivine - Peridot Wulfenite

Spinel Quartz (*)

Mineral Identification Basics• NON METALLICNON METALLIC LUSTER

Miscellaneous Lusters

Asbestos - Silky Apophyllite – Pearly (*)

Limonite - Dull or Earthy Sphalerite - Resinous

Graphite has a greasy or submetallic luster and easily marks paper. (*)

Mineral Identification Basics• PHYSICAL PROPERTIES LUSTER

This piece of Native Copper is severely weathered. It does not

look metallic. (*)

This is the same piece but the left side has been buffed with a steel brush. Note the bright metallic

luster. (*)

The moral to this story is to look at a

fresh surface whenever possible.

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The moral to this story is to look at a

fresh surface whenever possible.

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Mineral Identification Basics• PHYSICAL PROPERTIES COLOR

The COLOR of a mineral is usually the first thing that a person notices when observing a mineral. However, it is normally NOT the best physical property to begin the mineral identification process. (*)

Following are some examples of color variation within mineral species followed by minerals that have a distinctive color: (*)

Various colors of CALCITE. (*)

Clear - Without Impurities

Mineral Identification Basics• PHYSICAL PROPERTIES COLOR

Various colors of Quartz.

Hematite Inclusions Chlorite inclusions

Amethyst

Ionic Iron

Quartz comes in a wide range of colors. It is very easily colored by even trace amounts of impurities. (*)

Some minerals do have a certain color associated with them. Here are some examples: (*)

Mineral Identification Basics• INDICATIVE COLOR

Turquoise

SulfurMalachite

RhodochrositeAzurite (*)

Mineral Identification Basics• PHYSICAL PROPERTIES SPECIFIC GRAVITY

The SPECIFIC GRAVITY of a mineral is a measure of the mineral’s density. It is related to the types of elements that make up the mineral and how they are packed into the mineral’s atomic structure. (*)

Gold in Quartz

Gold has a Specific Gravity of 19.2. It is 19.2 times the weight of an equal volume of water. Water has a Specific Gravity of 1. (*)


The SPECIFIC GRAVITY of a mineral is determined by weighing the specimen in air and then weighing it in water. Here is the formula: (*)

(Weight in air) - (Weight in water )

Weight in airSpecific Gravity =

(*)

(divided by)


Triple Beam Balance

This is the equipment used in the lab at GCC to determine Specific Gravity. (*)


The first thing to check in using the balance is to make sure it balances at the zero mark when the tray is empty. (*)

This circle shows the zero mark and that the balance is calibrated correctly. (*)


Balance is in “Balance” (*)

Notches (*)

NO Notches (*)Notice that the top three bars of the balance have notches. These are the positions in which the weights are REQUIRED to rest. (*)


The bottom bar has no notch. Instead the weight (the small chrome sleeve sitting over the zero mark on the left) simply

slides along this bar. It reads 0.1 to 0.01 grams. (*)

NO Notches (*)


Selecting the right material. (*)

Sphalerite

Opal in Rhyolite

Calcite with Garnet

HaliteLimonite

Not just any mineral will do. In determining the specific gravity of a mineral it must be pure, free of pockets or cracks (places that can trap air) and it should not easily dissolve in water. (*)


Sphalerite

Opal in Rhyolite

Calcite with Garnet

HaliteLimonite

The Limonite is full of pore spaces. It is almost like a sponge. When it is weighed in water it has numerous trapped air pockets that will make it lighter that it should be. (*)

It would be difficult to get an accurate weight. (*)


Sphalerite

Opal in Rhyolite

Calcite with Garnet

HaliteLimonite

This is not a pure specimen. It is a combination of two minerals. The result of the specific gravity process would only give you an average of the two minerals. (*)


Sphalerite

Opal in Rhyolite

Calcite with Garnet

HaliteLimonite

The opal in rhyolite has the same problem as the calcite with garnet. It is not a pure sample (*)


Sphalerite

Opal in Rhyolite

Calcite with Garnet

HaliteLimonite

Halite is a salt. When weighed in water it dissolves. It would be difficult to get an accurate reading as it would become lighter and lighter as it slowly dissolved. (*)


Sphalerite

Opal in Rhyolite

Calcite with Garnet

HaliteLimonite

Sphalerite (pronounced: sfal er ite) is a good choice. It is a pure sample with no crack or pore spaces. And, it does not dissolve in water. (*)

Sphalerite


Determine the weight of the Sphalerite

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100 grams is too much.

Weight in air = 37.0 grams (*)


Weight in Water

The weights are in the same place but now that the sphalerite is submerged in water it is lighter, and the balance is again out of balance. (*)


Weight in Water

It is important to note that the specimen being weighed is not resting on the bottom of the beaker or touching its sides. It is also completely submerged beneath the water. (*)


Weight in Water (*)

0 grams

0.94 grams

7 grams20 grams

The weight of the sphalerite in water is 27.94 grams. (*)






37.00 grams

27.94 grams37.00 grams

4.06Specific Gravity = Note that there are no units. The grams cancel out. This is a ratio of how heavy the mineral is compared to an equal volume of water. The sphalerite is 4.06 times heavier than water. (*)

Mineral Identification Basics• PHYSICAL PROPERTIES TASTE

IT IS NOT RECOMMENDED THAT A TASTE TEST BE PERFORMED ON MINERALS AS A STANDARD PROCESS. SOME MINERALS ARE TOXIC.

However, the mineral HALITE is common salt and has a unique taste. (*)

Halite cubes from Trona, CA (*)

Mineral Identification Basics• PHYSICAL PROPERTIES MAGNETISM

MAGNETISM is the ability of a mineral to be attracted by a magnet. This most commonly is associated with minerals rich in

iron, usually magnetite. (*)

This is a piece of MAGNETITE with a magnet adhering to it. Magnetite is a mineral that is strongly magnetic in that a magnet will easily be attracted to it. (*)


More sensitivity is achieved if instead of a large sample, small pieces are used. In this way, even weakly magnetic minerals will be attracted to the magnet. (*)


This is a sample of “black sand” from Lynx Creek, Arizona. Its dark color is due to its high concentration of magnetite. See what happens when a magnet is place beneath the bottom right portion of the paper. (*)

This technique is used to separate out much of the unwanted material in the search for gold in placer deposits. (*)


LODESTONE is a variety of Magnetite that is naturally a magnet. (*)

Mineral Identification Basics• DOUBLE REFRACTION

DOUBLE REFRACTION: Is a property shared by many minerals ( but not those in the isometric crystal system). It is produced by the separating of a beam of light as it passes through the crystal structure. It is best displayed in the mineral CALCITE. This image clearly shows the double image below the calcite. (*)

Mineral Identification Basics• CHEMICAL PROPERTIES

REACTION TO HYDROCHLORIC ACID

Some minerals, notably the carbonates, react to cold dilute HCl. In this illustration a piece of CALCITE is shown to react (fizz) after HCl is applied. (*)

Calcite Reacts to HCl (*)

physical science 120 physical properties of minerals

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