字幕列表 影片播放 列印英文字幕 What is a mineral? A mineral is the basic building blocks all rocks. Different mineral mixes reveal the rocks origin and give the rock its name. Geologists and Mineralogist, who are scientists who study minerals and mineral formation, have identified and named over 6,000 different minerals. Minerals come in a rainbow of different colors and crystal structures. A mineral must meet five qualities to be considered a mineral. A mineral is solid. A mineral is naturally occurring. That means it's never man-made A mineral has an inorganic origin. that means that the mineral comes from non-living things. A mineral has a crystal structure. The atoms that make it up have a regular repeating pattern. A mineral has a definite chemical formula. The atoms that make it up will always be the same Silica will always be SiO2 and calcite will always be CaCO3 Rocks are made-up of minerals. Minerals are not rocks. The most valuable minerals tend to be metal ores, or minerals that we can extract metals from. Many minerals contained metallic elements which can be extracted which can be extracted Other minerals are useful for their chemical compounds in flavoring our food Salt is a prime example it comes from mineral halite. graphite is using a number of products including the core of pencils. Still other minerals are prized for their beauty and elegance Gemstones and jewelry are just a few of these treasures. Due to the huge number of minerals in the world Geologists use several different tests to determine the identity as a mineral. The first and most basic is color The problem with color is that small impurities within the crystal structure can dramatically change the appearance of a mineral. In addition several minerals may share the same color. Green is a very common color among minerals which contained copper. A small amount of titanium can change colorless diamond blue. The next test which can be performed is density. Density is a measurement of the ratio of a minerals mass to its volume. The more mass contained in a given volume the greater the density. We calculate density as a ratio of mass to volume. First we measure the mass a mineral sample using a balance. Because mineral samples are usually unevenly shaped, we can use the water displacement method to determine the volume of the sample. The graduated cylinder here has three hundred milliliters of water in it. When we add the mineral sample to the cylinder, it now reads 375 milliliters. The seventy five milliliter increase is the volume the sample took up. Density can then be calculated by dividing the mass by the volume. Crystal structure is a repeating geometric configuration having straight edges and flat faces. The atoms within a mineral are arranged in an ordered repeating way. Crystals can be very small and not always visible to the human eye. But all minerals will have a crystal structure. An eerie calm rolls across some barren stretch of land. but deep within the earth something strange and beautiful is happening. Within moments, rumblings from below break the silence. And in a tremendous explosion of fire and heat molten lava spews forth in all directions, bearing witness to the fury below. Within the earth's molten liquid rock, Minute particles called atoms dance wildly in every direction. As this molten mass cools, the movement of atoms slows down, and similar atoms begin bonding themselves together in an orderly fashion. This process is called crystallization. Which results in the formation of solid minerals. If conditions are just right, atoms of the same minerals and will continue to bond together creating wondrous crystal shapes. These crystal forms represent an outward expression of the internal arrangement of atoms. But what happens when two or more minerals of different types. crystallized together? We'd have the birth of a common rock The shape and structure at the Crystal reflects the pattern or arrangement atoms and molecules found within the mineral. Crystals are divided into six patterns. Ranging from simple cubic shapes, to complex multi-sided shapes. Depending on how the atoms within a crystal are arranged, a mineral can have very different hardness properties. Hardness is the scratchability of a mineral. We use the Moh's hardness scale of minerals to give a numeric value to the hardness of a mineral. The Moh's scale uses a set of 10 common index minerals ranging from talc, used in baby and body powder, at 1 to diamonds, the world's hardest known material, at 10. We use this set have known materials to scratch an unknown sample and then compare the results against the Moh's hardness scale. Index mineral 1 does not scratch the sample. The sample is harder than a 1. Index mineral 2 does not scratch the sample So the sample is harder than a 2. Index minerals 3 does not scratch the sample. So the sample is harder than a 3. index mineral for Index mineral 4 does not scratch the sample. The sample is harder than a 4. Index mineral 5 does not scratch the sample. The sample is harder than a 5. Index mineral 6 does not scratch the sample. So the sample is harder than a 6. Index mineral 7 does scratch the sample. See the little scratch? That means that the mineral sample is softer than a 7. Halfway between 6 and 7 is 6.5 The mineral has a hardness of 6.5. The next test to consider is luster. Luster is how light reflects off a crystal face. Luster is divided into two categories either metallic or non-metallic. Metallic lusters look like metal non-metallic lester's Non metallic lusters do not. Luster- the way light is reflected from the mineral's surface. Waxy, Metallic earthy, and vitreous are all words used to describe luster. Because color can be unreliable, scientists use a streak test to determine the true color of a mineral. Minerals can react with the atmosphere and appear very different to their true color The streak is the color of the powdered mineral. Streak is usually found by rubbing a mineral sample against a piece unglazed porcelain. Minerals harder than the streak plate, which has a hardness of 7, will not have a streak because the plate is not hard enough to grind up the mineral sample. When a mineral breaks it can break in one of two ways: it can cleave or it can fracture. Cleavage is a tendency is a mineral to break along flat plains and straight lines A mineral may have cleavage in only one direction, such as mica, which breaks off into thin sheets. There can be two directions of cleavage. Creating breaks that have two flat surfaces and one jagged surface. This is a way that feldspars break. Lastly, you can have three planes of cleavage, creating cubes or rhombahedrons. Galena and Halite both have three planes of cleavage and break into small cubes when broken. Look at this mineral sample. When broken with a hammer, small flat pieces up the sample flake off. Because these pieces have flat plains and surfaces the mineral shows cleavage when broken. If a mineral does not have cleavage, it has fracture. Fracture occurs when a mental breaks in an uneven or rough way. Quartz does not cleave, instead it fractures with a rough and uneven edge. This specific type of fracture shown by quartz is called concoidal fracture. fracture Look at this mineral sample. When broken with a hammer uneven and irregular pieces are broken off. These pieces have no flat plains or surfaces. instead they're completely irregular. This mineral shows fracture, not cleavage. There are several other tests that can help identify a mineral. Some minerals such as fluorite and some samples of calcite will fluoresce under ultraviolet light. Magnetite an iron ore is magnetic, hence its name Sulfur has a particularly pungent smell and is recognizable as the smell of matches as well as brimstone. Many carbonate minerals react to acid by creating carbon dioxide which fizzes and effervescences on the surface. Halite, or sodium chloride NaCl, taste like salt, because it is salt. However it's not a good idea to lick minerals, the sample could have been in contact with many hands and you wouldn't wanna lick all those people.