Which picture is a mineral? Why? The one on the left
Minerals Atoms make CRYSTALS, crystals make MINERALS, and minerals make ROCKS!!!!
Rocks vs. Minerals • Rocks: a solid combination of minerals or mineral materials. • Minerals: a naturally occurring, inorganic solid with a crystal structure and a characteristic chemical composition. There are roughly 4000 different minerals that have been identified!!!!!
Classifying Minerals 2 Groups of minerals Non-Silicates Silicates Will always be composed of an Silicon - Oxygen tetrahedron No silicon – oxygen tetrahedron present
SILICATES Have the fundamental building block SILICON-OXYGEN TETRAHEDRON 4 oxygen atoms around one silicon These tetrahedra can join in the following shapes: Sheets, chains, or three-dimensional networks Large silicate structures are than connect by: Fe, Mg, K, Na, and Ca
How Silicate Form A Silicate will crystallize From hot liquid magma @ Earth’s surface….low temperature and pressure @ great depths within the Earth….high temperature and pressure Small crystal size Larger crystal size Silicate minerals have the structure and a chemical composition that indicate the conditions under which it formed.
Properties of Minerals • Crystal Structure • Color • Streak • Luster • Density • Hardness • Fracture and Cleavage • Other Properties
Crystal Structure • Geometric shape All minerals are structurally built thru IONIC BONDS OR CRYSALLINE LATTICES!!!! • Each mineral always has the same crystal structure • Size may vary • Many form long prisms with a specific number of sides • Shapes include: cubes, sheets, needles, or threads Cubic crystals 6 sides 12 sided crystals All minerals are structurally built thru IONIC BONDS OR CRYSTAL LATTICES!!!!
Mineral Identification Basics • PHYSICAL PROPERTIES CRYSTALS A CRYSTAL is the outward form of the internal structure of the mineral. The 6 basic crystal systems are: (*) ISOMETRIC HEXAGONAL TETRAGONAL ORTHORHOMBIC MONOCLINIC Drusy Quartz on Barite TRICLINIC (*)
Top View (*) ORTHORHOMBIC ISOMETRIC MONOCLINIC TETRAGONAL HEXAGONAL The 6 basic crystal systems TRICLINIC
Color • Can be deceptive – slight changes in composition can cause significant change in a minerals color. Pyrite – Golden Color Quartz – pure – white impurities – violet Sulfur – Yellow
Streak • Color of a mineral’s powder • Can be found by scraping the mineral on a piece of unglazed porcelain (streak plate) • Not always same color as mineral Hematite Mineral is black or slivery Streak is red-brown
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. (*) 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. (*) Sphalerite has a light yellow streak. (*)
Luster • The way in which its surface reflects light. • Refers to general appearance of a mineral – how shiny it is. Galena – metallic Limonite – earthy Sulfur – greasy Halite - glassy
Mineral Identification Basics • PHYSICAL PROPERTIES LUSTER LUSTERis defined as the quality of reflected light. Minerals have been grossly separated into either METALLIC or NON-METALLIC lusters. Following are someexamples: (*) Native Silver has a Metallic Luster. (*)
Hardness • The resistance of a mineral to scratching. • A hard mineral can scratch a softer mineral, but not the other way around. Finger nail = 2.5 Copper penny = 3.5 Glass plate = 5.5
Mineral Identification Basics • PHYSICAL PROPERTIESHARDNESS 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. (*) 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. (*) Quartz is harder than glass.
Fracture & Cleavage • Fracture – how the mineral breaks generally jagged and uneven • Cleavage – type of fracture in which it tends to split along regular, well-defined planes (flat surfaces) Mica – breaks as sheets Halite – breaks as block chunks
Mineral Identification Basics • PHYSICAL PROPERTIES CLEAVAGE 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. (*)
Fluorite has cleavage in four directions. (*) Mica has perfect cleavage in ONE direction. (*) A thin sheet of Muscovite seen on edge. Mineral Identification Basics These pictures show different cleavage angles and the quality of cleavage. • PHYSICAL PROPERTIES CLEAVAGE
Rhombohedral Cleavage - 3 directions CALCITE Mineral Identification Basics (*) • PHYSICAL PROPERTIES CLEAVAGE Even these tiny fragments have rhombohedral cleavage. (*)
Examples of cleavage: If a mineral breaks easily and cleanly in one or more directions, its cleavage is considered perfect. For example, calcite cleaves perfectly along three planes. As the quality of the break decreases, cleavage may be described as good, distinct, and poor or none. Some minerals cleave perfectly in one direction and poorly in others.
Examples of Fracture: Not all minerals cleave easily. Some fracture instead. Unlike cleavages, which are usually clean, flat breaks, fractures can be smoothly curved, irregular, jagged or splintery. Conchoidal fracture results in a series of smoothly curved concentric rings about the stressed point, generating a shell-like appearance Non-conchoidal fracture results in a rough, rugged surface. Non-conchoidal examples conchoidal fracture, which is a smooth but curved fracture surface resembling the interior surface of a shell
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 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 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. (*) Gold in Quartz
Mineral Identification Basics The SPECIFIC GRAVITY of a mineral is determined by weighing the specimen in air and then weighing it in water. Here is the formula: (*) • PHYSICAL PROPERTIES SPECIFIC GRAVITY Weight in air Specific Gravity = (Weight in air) - (Weight in water ) (divided by) (*)
Mineral Identification Basics • PHYSICAL PROPERTIES SPECIFIC GRAVITY Triple Beam Balance This is the equipment used in the lab at GCC to determine Specific Gravity. (*)
Mineral Identification Basics Selecting the right material. (*) • PHYSICAL PROPERTIES SPECIFIC GRAVITY Opal in Rhyolite 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. (*) Calcite with Garnet Sphalerite Limonite Halite
Mineral Identification Basics 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. (*) • PHYSICAL PROPERTIES SPECIFIC GRAVITY Opal in Rhyolite Calcite with Garnet Sphalerite Limonite Halite It would be difficult to get an accurate weight. (*)
Mineral Identification Basics 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. (*) • PHYSICAL PROPERTIES SPECIFIC GRAVITY Opal in Rhyolite Calcite with Garnet Sphalerite Limonite Halite
Mineral Identification Basics The opal in rhyolite has the same problem as the calcite with garnet. It is not a pure sample (*) • PHYSICAL PROPERTIES SPECIFIC GRAVITY Opal in Rhyolite Calcite with Garnet Sphalerite Limonite Halite
Mineral Identification Basics 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. (*) • PHYSICAL PROPERTIES SPECIFIC GRAVITY Opal in Rhyolite Calcite with Garnet Sphalerite Limonite Halite
Mineral Identification Basics 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. (*) • PHYSICAL PROPERTIES SPECIFIC GRAVITY Opal in Rhyolite Calcite with Garnet Sphalerite Sphalerite Limonite Halite
Mineral Identification Basics 100 grams is too much. • PHYSICAL PROPERTIES SPECIFIC GRAVITY Weight in air = 37.0 grams (*) Determine the weight of the Sphalerite (*)
Mineral Identification Basics Weight in Water • PHYSICAL PROPERTIES SPECIFIC GRAVITY 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. (*)
Mineral Identification Basics Weight in Water • PHYSICAL PROPERTIES SPECIFIC GRAVITY 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 air Weight in air Specific Gravity = Specific Gravity = (Weight in air) - (Weight in water ) (Weight in air) - (Weight in water ) Mineral Identification Basics • PHYSICAL PROPERTIES SPECIFIC GRAVITY 37.00 grams 37.00 grams 27.94 grams Specific Gravity = 4.06 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 The manner in which minerals transmit light is called DIAPHANEITY and is expressed by these terms: (*) • PHYSICAL PROPERTIES DIAPHANEITY TRANSPARENT: A mineral is considered to be transparent if the outline of an object viewed through it is distinct. (*) TRANSLUCENT: A mineral is considered to be translucent if it transmits light but no objects can be seen through it. (*) OPAQUE: A mineral is considered to be opaque if, even on its thinnest edges, no light is transmitted. (*) Quartz with Spessartine Garnets