Minerals

Minerals• This term is used in several different ways.• Health and fitness – extol the benefits of

it together with vitamins.• Mining Industry – for anything taken out

of the ground (such as coal, iron core or sand and gravel).

• Geologist – any naturally occuring inorganic solid that possesses an orderly crystalline structure and a well defined chemical composition.

Characteristic of Minerals ( According to Geologist)

• Naturally occurring – It means that a mineral should be formed by natural geologic processes.– This is why synthetic diamonds and

rubies, as well as variety of other usefuk materials produced by chemist are not considered as minerals

Characteristic of Minerals ( According to Geologist)

• Solid – In order for something to be considered as mineral, it should be solid at temperatures normally experienced at Earth’s surface.– Thus, Ice (Frozen water) is considered as

mineral whereas liquid water is not.

Characteristic of Minerals ( According to Geologist)

• Orderly Crystalline Structure – Minerals are crystalline substances which means their atoms are arranged in an orderly, repetitive manner.

• This orderly packing of atoms is reflected in the regularly shaped objects we call crystals.

• Some Naturally occurring solids, such as volcanic glass (obsidian), lack a repetitive atomic structure and are referred to as amorphous (without form) and are CONSIDERED AS MINERALS.

Characteristic of Minerals ( According to Geologist)

• Well-defined Chemical Composition – Most minerals are chemical compounds made up of two/more elements. A few (such as Gold and Silver) consist of only a single element.

• The common mineral quartz consist of 2 oxygen (O) atoms for every Silicon (Si) atoms, giving it a chemical composition expressed by the formula SiO2. Thus, no matter what the environment is, whenever atoms of Oxygen and Silicon joined together in the rato of 2 to 1, the product is always quartz.

Characteristic of Minerals ( According to Geologist)

• Generally InorganicInorganic – Substances such as stone and

metal that do not come from living things.• Minerals are generally inorganic. Inorganic

crystalline solids, as exemplified by ordinary table salt (Halite) that are found naturally are considered minerals.

• Organic Compounds on the other hand, are generally not.

• Ex. Sugar – (Crystalline like salt) comes from sugarcane or sugar beets and is common example of such an organic compound.

Chemical Composition of Minerals

• Minerals and other earth materials are composed of chemical elements.

• Elements – Fundamental component of matter that cannot be broken into a simpler particles by ordinary chemical processess. (Most common minerals consist of a small number – usually 2 to 5 of different chemical elements).

Eight Most Abundant Chemical Elements in Earth’s Crust:

• Oxygen• Silicon• Aluminum• Iron• Calcium• Sodium• Potassium• Magnesium

• In nature, most chemical elements have either a positive (+) ornegative (-) charge.– ION- atom with either positive/negative

charge– CATION – Positively charged atom– ANION – Negatively charged atom

• Most minerals are made up of 2-5 essential elements. Ex. Formula of quartz is SiO2. One atom of Silicon for every 2 atoms of oxygen.

The Crystalline Nature of Minerals

• The mineral has a crystalline structure, and therefore every mineral is a crystal.

– Crystal – any solid element/compound whose atoms are arranged in a regular, periodically repeated manner

Ex. Mineral halite (common table salt)

• NaCl– One sodium for every one chlorine

Figure 1.1

(You can see here that the sodium & chlorine ions alternate in orderly rows & columns intersecting at right angles. Figure 1.1 is the crystalline structure of halite).

• Crystalline Structure - orderly, repetitive arrangement of atoms in a crystal.

Salty sea water evaporates from tidal pool

As evaporation continues, more and more sodium& chlorine ions would precipitate onto the faces of the growing crystal.

• Crystal Face – flat surface that develops if a crystal grows freely in an uncrowded environment. Under perfect conditions, the crystal that forms will be symmetrical.– Symmetrical – has a corresponding

similar parts: in other words, one side is the same as the other.

Physical Properties of Minerals

• This properties allow geologists to identify a mineral in the field.– Chemical composition– Crystal structure

• But if you pick a crystal of a mineral( for example, halite), you cannot see the atoms. You should measure its chemical composition and crystal structure by laboratory procedures, but such analyses are expensive & time consuming.

• Geologists commonly use properties to identify minerals.

Physical Properties of Minerals

• Crystal Habit – characteristic shape of an individual crystal & the manner in w/c aggregates of crystals grow.

Geologists can identify that this mineral is a prismatic quartz because of its elongated shape. 

Physical Properties of Minerals

• Cleavage – tendency of some minerals to break along that surface, which are planes of weak bonds in the crystal. When a mineral has excellent cleavage, sheet after sheet can be peeled from the crystal, like peeling layers from an onion.

Cleavage

Physical Properties of Minerals

• Fracture – a manner n which minerals break other than along planes of cleavage.

The type of fracture shown in this picture is concoid.

Physical Properties of Minerals

• Hardness – resistance of a mineral to scratching & is one of the most commonly used properties for identifying a mineral.

• Mohs Hardness Scale – after Friedrich Mohs, he developed this scale in the early 19th century.

Mohs Hardness Scale

This scale was used to measure the hardness of a mineral more accurately.

Mineral Hardness scale 1-10: 

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Physical Properties of Minerals

• Color – most obvious property of a mineral is often used in identification. But color can be unreliable because small amount of chemical impurities can dramatically alter color.

Physical Properties of Minerals

• Streak – refers to the color of the fine powder of a mineral. It is observed by rubbing the mineral across a piece of unglazed porcelain known as the “streak plate”.

• Streak • Streak Plate

Physical Properties of Minerals

• Luster – manner in which a mineral reflects light. A mineral with a metallic look irrespective of color has a metallic luster. As a result, it looks like gold & is commonly called “fool’s gold”.

Pyrite Mineral

Luster

•Metallic - Minerals with a metallic luster are opaque and reflective, like metal. The metallic elements, most sulfides, and some oxides belong in this category.

•Opaque-

• chalcopyrite500

Luster

• Pearly - Describes a luster similar to the inside of a mollusk shell or shirt button.

Luster

• Earthy- This luster defines minerals with poor reflective qualities, much like unglazed porcelain. Most minerals with a dull luster have a rough or porous surface.

• Porous- Containing rounded, tiny holes throughout. Porous minerals are lightweight and easily dyed.

Luster

• Resinous - This is the luster of many yellow, dark orange, or brown minerals with moderately high refractive indices - honey like, but not necessarily the same color.

• Refractive indices- The amount of refraction that takes place in a particular substance, which is a direct connection to the speed of light in that substance.

Other Properties:

• Reaction to acid

• Magnetism

• Radioactivity

• Fluorescence - FluorescenceProperty exhibited in certain minerals in which they display a glowing effect when having ample illumination with ultraviolet light.

• Phosphorescence- Phosphorescence• The ability of some fluorescent minerals

to keep on glowing for several seconds after the fluorescent lamp has been removed. 

• these properties can be characteristics of specific minerals

Mineral Classes

• Geologists classify according to their chemical elements.

• Silicates, together w/ oxygen make up about 42% of earth’s crust. They are abundant for 2 reasons. First, silicon & oxygen are the two most plentiful elements in the crust. Secondly, silicon & oxygen combine readily.

Carbonates

• Carbonate minerals are much less common than silicates n earth’s crust, but they are important rock-forming minerals because they form sedimentary rocks that cover large regions of every continent. The shells & other hard parts of the most marine organisms such as clams, oysters & corals are made of carbonate materials.

Commercially Important Minerals

• Commercially Important Minerals are minerals from which metals / other elements can be profitably recovered.

• Industrial minerals - rocks/ minerals that have economic value exclusive of metal ones, fuels & gems.

• Gem – mineral that is priced primarily for its rarity and beauty although some gems such as diamonds are also used industrially.

•   Precious Gems- Any of several gems, including the diamond, emerald, ruby, and sapphire, that have high economic value because of their rarity or appearance.

Precious gems

Semi-precious Gems