How minerals form. September 20, Mineral families and formation.notebook

Transcription

1 How minerals form Minerals form (primarily) in 3 different ways: 1. From the cooling and hardening of magma and lava Oct 20 7:06 AM Whether the rock melt cools quickly or slowly, ions and elements within the melt combine to form minerals. The minerals that form depend on the type of elements in the melt, the rate of cooling and several other factors Oct 20 7:25 AM 2. Minerals form when mineral rich water evaporates, leaving the minerals dissolved within the water behind. Oct 20 7:26 AM 1

2 Gypsum fields and travertine Oct 20 7:31 AM Salt mines Oct 20 7:32 AM Oct 20 7:33 AM 2

3 Gold veins found within quartz Oct 20 7:41 AM 3. Minerals form when existing rock gets heated (from any number of processes) such as a. proximity to a magma chamber b. Friction along faults c. Pressure deep within the crust d. Chemical reaction when in contact with very hot water Oct 20 7:31 AM In this case, the rock does NOT melt, it simply softens enough for ions, molecules and elements to be able to move and recombine to form different minerals that what previously existed in the rock. Oct 20 7:30 AM 3

4 In this case, the minerals recombine in bands that are perpendicular to the frictional or pressure force Oct 20 7:27 AM In most cases the rocks become denser and their crystals enlarge like this marble Oct 20 7:39 AM The crystal structure is the form the mineral takes when it's atoms arrange themselves in an orderly pattern. There are 6 crystal shapes. Crystal shape and a mineral's cleavage/ fracture are NOT the same. A good example is QUARTZ: quartz has a beautiful hexagonal crystal shape, but when struck with a hammer, the mineral will fracture rather than break along a smooth cleavage plain. This is because there are no weaker areas among the bonds along which quartz can break smoothly. Oct 20 7:40 AM 4

5 Oct 20 7:27 AM A minerals' crystal structure (or how the atoms are arranged and how tightly or strongly the bonds between the atoms are) CAN effect several characteristics, however: Oct 20 7:54 AM Let's use 2 well known minerals of the same chemical composition to better understand this... Oct 20 9:15 AM 5

6 Oct 20 8:00 AM It can effect hardness of a mineral Graphite vs. Diamond is a good example here. It can effect the density of a mineral The closer packed the atoms of a mineral are the denser it will be: again, compare the density of graphite to diamond, the density of a diamond is 3.5 g/cm3 while graphite is 2.2g/cm3 Oct 20 7:55 AM It can effect whether the mineral will exhibit cleavage or fracture. in some cases, a mineral will cleave along weak bonds that correspond to a crystal plain. Calcite and halite are good examples of minerals that exhibit cleavage along their crystal faces Oct 20 7:53 AM 6

7 MINERAL GROUPS There are 4 major groupings of minerals: 1. Silicates (by far the LARGEST group of minerals, they make up 90% of all the minerals in Earth's crust! The primary building block of the silicates is the silica tetrahedron SiO4, and are classified by how the tetrahedrons are linked together. Oct 20 7:27 AM Quartz and Feldspar Oct 20 8:41 AM 2. Carbonates: Although not as common as the silicates, (obviously) several carbonates (non silicates) are commonly found in Earth's crust. Carbonates are composed of a carbonate ion bonded with a positive metal ion. (a carbonate ion is a one carbon atom covalently bonded with 3 oxygen atoms) Oct 20 7:23 AM 7

8 Calcite is a mineral that is a carbonate and has great cleavage! Oct 20 8:43 AM 3. Oxides: Oxides are rather uncommon minerals, but important because they are economically useful as ores Oxides are minerals that contain a lot of the element iron bonded with an oxygen atom Oct 20 9:19 AM Hematite and magnetite are examples of minerals in the oxide family Oct 20 9:24 AM 8

9 4. Sulfides: Like oxides, sulfides are rather uncommon, but used as ores of iron and other valuable metals. A sulfide is composed of a sulfur atom bonded with a positive metal ion Oct 20 9:29 AM Pyrite is the most common sulfide It's so pretty!!!!! Oct 20 9:28 AM 9