Minerals

Minerals: 

Minerals

What is a Mineral?: 

What is a Mineral? Naturally Occurring forms by natural geologic processes Solid Substance solid within Earth’s normal temperature ranges Orderly Crystalline Structure atoms or ions are arranged orderly & repetitive Definite Chemical Composition chemical compounds of two or more elements Generally Considered Inorganic Inorganic substances found in nature

How Minerals are Formed: 

How Minerals are Formed Crystallization from Magma Precipitation Changes in Pressure and Temperature Hydrothermal Solutions

Crystallization from Magma: 

Crystallization from Magma Magna or molten rock forms deep in the Earth. As magma cools, elements combine to form minerals. First to crystallize are minerals rich in iron, calcium and magnesium. Later minerals rich in sodium, potassium and aluminum form. Muscovite Feldspar Quartz Hornblende

Precipitation: 

Precipitation Water contains many dissolved substances. Evaporation causes these substances to be left behind as minerals. Changes in water temperature can also cause dissolved material to precipitate out as minerals. Limestone , Calcite and Halite are minerals that form by precipitation. Calcite Halite Limestone

Changes in Pressure and Temperature: 

Changes in Pressure and Temperature Existing minerals when subjected to changes in pressure & temperature form new minerals. Pressure increase causes minerals to recrystallize or form more compact minerals. Temperature increase causes some minerals to become unstable, forming new minerals stable at the new temp. Muscovite Talc

Hydrothermal Solutions: 

Hydrothermal Solutions A hydrothermal solution is a hot mixture of water & dissolved substances. Hydrothermal solutions have temps between 100°C and 300°C. When these solutions contact existing minerals, chemical reactions occur that form new minerals. Bornite Chalcopyrite

Mineral Groups: 

Mineral Groups Silicates Carbonates Oxides Sulfates and Sulfides Halides Native Elements

Silicates: 

Silicates Silicon & Oxygen are two most abundant elements in Earth’s crust. They combine to form the silicon-oxygen tetrahedron which consists of one Silicon atom and four Oxygen atoms. Quartz is the most common silicate mineral. Silicon-oxygen tetrahedron Quartz

Silicate Structures: 

Silicate Structures Silicon-oxygen tetrahedra can join in many ways. Olivine is made up of millions of single tetrahedra. In Augite , the tetrahedra form single chains. Hornblende forms double chains. In Mica the tetrahedra join to form sheets.

Carbonates: 

Carbonates Second most common mineral group. Contains carbon, oxygen and one or more other metallic element. Calcite is the most common carbonate mineral. Dolomite contains magnesium and calcium. Calcite Dolomite Marble

Oxides: 

Oxides Minerals that contain oxygen and one or more other metals. Rutile is titanium oxide, forms as magma cools deep in the Earth. Corundum is aluminum oxide, forms from pressure & temperature changes. Hematite is an iron oxide, forms when minerals are exposed to water or moisture in the air. Rutile Corundum Hematite

Sulfates and Sulfides: 

Sulfates and Sulfides Minerals that contain the element sulfur. Sulfates like Anhydrite & Gypsum form when mineral-rich waters evaporate. Sulfides like Galena & Pyrite form from thermal solutions. Pyrite is often called “fools gold”. Anhydrite Gypsum Galena Pyrite

Halides: 

Halides Minerals that contain a halogen ion plus one or more other elements. Halogens are elements from Group 7A of the periodic table. Includes the elements fluorine and chlorine. Halite or table salt is one of the most common halides. Fluorite is a common halide used in making steel. Halite Fluorite

Native Elements: 

Native Elements A group of elements that exist in relatively pure form. Native elements include Gold , Silver , Copper , Sulfur , and carbon. Native forms of carbon are Diamond and Graphite . Some native elements are formed from hydrothermal solutions. Gold Silver Graphite Copper Sulfur Diamond

Properties of Minerals: 

Properties of Minerals The properties of minerals are used to identify them. These include…. Color Streak Luster Crystal Form Hardness Cleavage Fracture Density Double Refraction Acid Reaction Magnetism Feel, Smell, Taste

Color: 

Color One of the first things noticed about a mineral. Color is unique to some minerals, but often not useful in identifying many minerals. Small amounts of different elements can give the same mineral different colors.

Streak: 

Streak It is the color of a mineral in its powdered form. Obtained by rubbing a mineral across a streak plate of unglazed porcelain. Streaks rarely vary so it is a good indicator. Metallic minerals have a dense, dark streak. Streak plate with Pyrite (left) and Rhodochrosite (right)

Luster: 

Luster The way a mineral shines or how light is reflected from the surface of a mineral. Two main types of luster: metallic and non-metallic . Metallic luster has the shine of freshly polished metal. Non-metallic luster includes vitreous or glassy, pearly, silky, and earthy. Diamond has a adamantine or brilliant luster. A somewhat metallic appearance is a sub-metallic luster.

Luster: 

Luster Adamantine Diamond Pearly Muscovite Earthy Kaolin Silky Gypsum satin spar Sub-metallic Sphalerite Metallic Pyrite Vitreous Quartz

Crystal Form: 

Crystal Form It is the visible expression of a mineral’s internal atom arrangement. Each mineral has a distinct crystal form. If a mineral forms slowly without interference from neighboring grains, it will develop into regular geometric crystal shapes. Crowding prevents formation of well-formed crystals and results in a shapeless intergrown mass of small crystals.

Crystal Form: 

Crystal Form Quartz forms hexagonal or six-sided crystals. The ends of these crystals exhibit a pyramid shape. Fluorite usually forms cubic crystals.

Crystal Form: 

Crystal Form Beryl forms six-sided hexagons with flattened bases. Calcite is a 3 dimensional parallelogram called a rhomboid. Rhodochosite forms rhomohedrons or scalahedrons. Amethyst is a hexagonal prismatic that forms as individual scepters or aggregate clusters. Beryl Calcite Rhodochrosite Amethyst

Crystal Forms: 

Crystal Forms Galena Cubes Pyrite Pyritohedron Wulfenite Tabular Stibnite Prismatic Beryl Hexagonal Calcite Scalenohedron

Hardness: 

Hardness It is the measure of the resistance of a mineral to being scratched. One of the most useful properties in identifying a mineral. Rubbing a mineral against a mineral of known hardness will help determine the hardness of the unknown mineral. Geologists use a standard hardness scale called the Mohs scale .

Mohs Hardness Scale: 

Mohs Hardness Scale This scale consists of 10 minerals arranged from 10 (hardest) to 1 (softest). Calcite (3) , which can sometimes resemble Quartz, cannot scratch glass but Quartz (7) will scratch a glass plate. Diamond , the hardest mineral on Earth, can scratch anything.

Cleavage: 

Cleavage The tendency of a mineral to cleave, or break, along flat, even surfaces. In a mineral’s atomic structure, some bonds are weaker than others. The weaker bonds are places where a mineral will break when stressed. Mica has weak bonds in one direction and cleaves to form flat sheets. Halite has 3 directions of cleavage that meet at 90° angles. Calcite also has 3 directions of cleavage, but they meet at 75° angles.

Cleavage: 

Cleavage

Cleavage: 

Cleavage

Fracture: 

Fracture When minerals do not exhibit cleavage or split along a zone of weakness, the break is called a fracture. It is the uneven breakage of a mineral. There are several types of fracture: c onchoidal and subconchoidal earthy jagged or hackly splintery uneven

Fracture: 

Fracture Conchoidal fracture is curved break that resembles ripples of a clam shell. Most common type of fracture. Occurs in Quartz , Obsidian , Flint and Opal . Subconchoidal is similar, but not as curved. Quartz Obsidian

Fracture: 

Fracture Earthy fracture is similar to freshly broken soil. Occurs in soft, loosely bound minerals like Limonite , Kaolinite , and Aluminite . Jagged or Hackly fracture is jagged with sharp points and edges. Occurs when metals are torn. Found in Native Copper and Silver . Limonite Native Copper

Fracture: 

Fracture Splintery fracture is seen in fibrous minerals such as Chrysotile and in non-fibrous minerals with strong structure in one direction like Kyanite . Uneven fracture is self descriptive. Occurs in a wide range of minerals like Magnetite , Anhydrite , and Pyrite . Chrysotile Magnetite

Density: 

Density The ratio of a mineral’s mass to its volume. Density (D) = mass (m) / Volume (V) Most common minerals have densities between 2 and 5 g/cm³. Metallic minerals such as Copper , Galena and Gold usually have greater densities.

Double Refraction: 

Double Refraction Some minerals can split one beam of light into two beams. When you look at an object through one of these minerals, you see two images of the object. Calcite exhibits this property better than other minerals.

Acid Reaction: 

Acid Reaction Minerals containing carbonate (CO 3 )-² react when a drop of hydrochloric acid is placed on them. Bubbles of carbon dioxide gas appear on the surface of the mineral. Calcite (calcium carbonate) reacts readily.

Magnetism: 

Magnetism A few minerals are attracted to a magnet or are capable of acting as a magnet. The most common magnetic mineral is Magnetite . This property is so rare, it narrows the possibilities drastically when present.

Feel, Smell, Taste: 

Feel, Smell, Taste Some minerals such as Talc and Graphite , feel slippery or greasy when rubbed. Minerals such as Sulfur and Pyrite smell like rotten eggs. Kaolinite smells like fresh clay. Arsenic smells like garlic. Taste is one of the last tests to be done because some minerals are poisonous. Halite tastes salty. Sylvite tastes bitter. NEVER TASTE A MINERAL UNLESS INSTRUCTED TO DO SO!!!