Notes #_____анаClassifying Minerals and Rocks In order to be a

Notes #_____ ­ Classifying Minerals and Rocks In order to be a ​
mineral​
, a substance ​
MUST ❏ be naturally occurring (not man­made) ❏ be inorganic (cannot have ever been living or composed of things that were living) ❏ be a solid ❏ have a crystal structure (atoms that line up in a repeating pattern, crystals have flat sides, called faces, that meet at sharp edges and corners) ❏ have a definite chemical composition (always have the same element or elements combined in the same proportions) Each mineral has ​
characteristic properties​
that can be used to identify it. These properties include ● Color​
­ some minerals have unique coloring, but several minerals have a “gold” color, so color alone is not enough to identify a mineral. ● Streak​
­ the color of the mineral’s powder, sometimes the streak color is completely different than the color of the mineral itself! ● Luster​
­ describes how light is reflected off the mineral’s surface. Can be metallic, glassy, waxy/pearly, earthy, silky, or dull. ● Density​
­ density is the amount of mass in a given space. Minerals that are more dense can feel much heavier than a less dense mineral that is the same size. Remember, density = mass/volume ● Hardness​
­ using the Mohs hardness scale, ranks minerals based on their ability to scratch or be scratched by other minerals. ● Structure/Crystal systems​
­ number and angle of crystal faces (cubic, hexagonal, tetragonal, etc). ● Cleavage and Fracture​
­ minerals that split easily along flat surfaces have the property of cleavage, minerals that break in an irregular way are said to fracture. ● Special properties​
­ conductivity (ability to conduct electricity), magnetism, fluorescence (glowing under ultraviolet light), reactivity with acid or water, etc. When studying rock samples, geologists observe the rocks ​
mineral composition, color, and texture​
. Rocks can be made up of mixtures of minerals and other materials, several different minerals, and, rarely, a single mineral. Observing these characteristics tell geologists how the rock was formed which helps us learn about what Earth was like long ago. ● Mineral Composition and Color ○ Color provides us a clue as to what minerals are in the rock, but because many minerals are the same color, you cannot rely on color alone. ○ Geologists observe the shape of the minerals, as well as many of the tests listed above to identify the minerals in a rock. ● Texture ○ Most rocks are made up of particles or minerals or other rock, called grains. Grains give the rock its texture. Texture is the look and feel of the rock’s surface. ○ Grain Size ■ Grains that are large and easy to see = coarse grained ■ Grains that are too small to see without a hand lense or microscope = fine grained ■ Some rocks have no grains, even under the microscope, these are sometimes called glassy. ○ Grain Shape ■ Crystalline ­ shape of the minerals structure ■ Rounded or smooth ­ like pebbles or grains of sand ■ Jagged ­ grains have sharp edges and angles ○ Grain Pattern ■ Layered, like a stack of pancakes ■ Banded, like stripes of color ■ Non­banded, can have random arrangement