The Wild, Wacky World of Minerals

Group Activity: Classification

1. Observation of minerals

2. Group all minerals into three categories.

3. Explain why you chose these categories and how the minerals fit them.

Minerals: Building Blocks of Rocks

- Definition of a mineral:

•Naturally occurring

•Inorganic solid

•Ordered internal molecular structure

•Definite chemical composition

- Definition of a rock:

•A solid aggregate or mass of minerals

OK, so a mineral makes a rock. But, what makes a mineral?

Elements!

- Elements

•Basic building blocks of minerals

•Over 100 are known (92 naturally occurring)

Elements make minerals, and atoms

make elements!- Atoms

•Smallest particles of matter

•Retain all the characteristics of an element

Quick Recap!

Atoms make

Elements,

which make

Minerals, which

make

Rocks!

Physical Properties of MineralsOptical Properties

- Luster

-Ability to transmit light

- Color

- Streak

Shape Properties

-Crystal shape or habit

Strength Properties

- Tenacity

- Hardness

- Cleavage

- Fracture

Weight/Mass Properties

- Density

- Specific Gravity“Other” Properties

- Taste/Smell

- Texture

- Glow in the dark

-Acid reaction

- Magnetic

-Luster: The appearance or quality of light reflected from the surface of a mineral. Minerals with the appearance of metal are said to have a “metallic luster.” Other non-metal-like minerals have a nonmetallic luster, and are also known as vitreous/glassy, dull/earthy, pearly (like a pearl), silky (like a satin sheet), or greasy (as though covered in oil).

-Ability to transmit light: Can light shine through the mineral? If so, it might be considered transparent. If not, it could be called opaque. If light can shine through the mineral but not an image, it is called translucent.

-Color: Easiest property to spot; worst property to use in interpreting a mineral. Lots of minerals have the same color!

- Streak: The color of the powered mineral. Useful when you have several different colors of the same mineral. The streak will always be the same for a type of mineral.

Optical Properties

Examples of Optical Properties

-Luster:

-Ability to transmit light:

Metallic Metallic Non-Metallic Earthy/Dull GlassyPearly

TranslucentOpaque Transparent

- Color:

Examples of Optical Properties

- Streak:

- Crystal shape or habit: This refers to the common or characteristic shape of a crystal or aggregate of crystals. Some minerals tend to grow equally in three directions, while others tend to be elongated in one direction. Commonly used terms to describe these and other crystal habits include equi-dimensional, bladed, fibrous, tabular, prismatic, platy, blocky, and botryodial.

Shape Properties

Pyrite has two or more characteristic

habits

-Density: Density is an important property of matter defined as mass per unit volume, usually expressed as g/cm3.

Weight/Mass Properties

- Specific Gravity: Mineralogists use a related measure to density, called specific gravity, to represent the ratio of a mineral’s weight to the weight of an equal volume of water. With a little practice, you can estimate specific gravity by holding a mineral in your hand. If it feels about as “heavy” as similar-sized rocks you have held, the specific gravity of the sample will likely be between 2.5 and 3.

Quartz, a common rock-forming mineral, has a

specific gravity of 2.65.

Galena, a which is a metallic mineral and an ore of lead , has a specific gravity of 7.5.

-Tenacity: This describes a mineral’s toughness, or its resistance to breaking or deforming. Minerals that are ionically bonded, such as fluorite and halite, tend to be brittle and shatter into small pieces when struck. Minerals with metallic bonds, such as copper, are malleable, or easily hammered into different shapes.

-Hardness: One of the most useful diagnostic properties of minerals! This is the measure of the resistance of a mineral to abrasion or scratching. This property is determined by rubbing a mineral of unknown hardness against one of known hardness. A numerical value of hardness can be obtained by using the Mohs scale.

-Cleavage: This describes the tendency of a mineral to break (cleave) along planes of weaker bonding.

- Fracture: Minerals having chemical bonds that are equally, or nearly equally, strong in all directions exhibit a property called fracture. When minerals fracture, most produce irregular surfaces.

Strength Properties

Examples of Strength Properties

-Tenacity: -Hardness:

Malleable

Brittle

Sectile Elastic

-Cleavage:Where a mineral’s bonds will want to naturally break (kind of like cake layers).

Examples of Strength Properties

-Fracture:

Examples of Strength Properties

A description of a mineral whose bonds are equally, or nearly equally strong in all directions, causing it to break unevenly (like a loaf of bread).

The above is an example of conchoidal fracture. The smooth curved surfaces result when minerals break in a glasslike manner.

-Taste/Smell: Halite, which is ordinary salt, can be quickly identified through taste. Sulfur smells like rotten eggs, and is easily identified by smell.

-Texture: Talc and graphite have very distinctive feels. Talc feels soapy, and graphite feels greasy.

-Glow in the dark: Some minerals have a chemical composition that allow them to take on a fluorescent glow.

-Acid reaction: Certain minerals, called carbonates, will effervesce (fizz) as carbon dioxide gas is released. You can see the reaction by placing a drop of dilute hydrochloric acid on the mineral.

- Magnetic: A few minerals have a high iron content and can be picked up with a magnet.

“Other” Properties

Mineral Project!

Due Monday, Sept. 19

Also for Monday: Read Chapter 2