Greasy - Luster of a mineral that appears as if it were coated with grease. Pitchy - Minerals with a tar-like appearence have a pitchy luster.
Minerals with a pitchy luster are usually radioactive and have gone through the process of metamiction. Waxy - A waxy luster describes a mineral that appears as if it were coated with a layer wax. Dull - This luster defines minerals with poor reflective qualities, much like unglazed porcelain.
Most minerals with a dull luster have a rough or porous surface. Every mineral has a characteristic luster, but some minerals may have a different luster on different specimens. There is no scientific method to determine luster. Often, determining the luster of a particular specimen is personal; to some it may appear as one type of luster, and to others as a different type. It is in the eyes of the viewer to determine what luster a particular specimen exhibits.
Luster is only a useful form of mineral identification when the specimen in question displays a unique luster, such as waxy, greasy, pearly, etc. Specimens with a vitreous luster cannot be distinguished from one another, nor can minerals with a metallic luster. Color is readily observable and certainly obvious, but it is usually less reliable than other physical properties.
Figure 1. This mineral has shiny, gold, cubic crystals with striations, so it is pyrite. Mineralogists are scientists who study minerals. One of the things mineralogists must do is identify and categorize minerals. While a mineralogist might use a high-powered microscope to identify some minerals, most are recognizable using physical properties.
Check out the mineral in Figure 1. What is its shape? Are the individual crystals shiny or dull? Are there lines striations running across the minerals? Diamonds are popular gemstones because the way they reflect light makes them very sparkly.
Turquoise is prized for its striking greenish-blue color. Notice that specific terms are being used to describe the appearance of minerals. Figure 2. This mineral is shiny, very soft, heavy, and gold in color, and is actually gold. Color is often useful, but should not be relied upon.
Different minerals may be the same color. Real gold, as seen in Figure 2, is very similar in color to the pyrite in Figure 1. Additionally, Some minerals come in many different colors.
Quartz, for example, may be clear, white, gray, brown, yellow, pink, red, or orange. So color can help, but do not rely on color as the determining property. Figure 3 shows one sample of quartz that is colorless and another quartz that is purple. A tiny amount of iron makes the quartz purple. Many minerals are colored by chemical impurities. Figure 3.
Purple quartz, known as amethyst, and clear quartz are the same mineral despite the different colors. Mineralogists have special terms to describe luster. One simple way to classify luster is based on whether the mineral is metallic or non-metallic. Minerals that are opaque and shiny, such as pyrite, have a metallic luster. Minerals such as quartz have a non-metallic luster. Luster is how the surface of a mineral reflects light. It is not the same thing as color, so it crucial to distinguish luster from color.
Standard names for luster include metallic, glassy, pearly, silky, greasy, and dull. It is often useful to first determine if a mineral has a metallic luster. A metallic luster means shiny like polished metal.
For example cleaned polished pieces of chrome, steel, titanium, copper, and brass all exhibit metallic luster as do many other minerals. Of the nonmetallic lusters, glassy is the most common and means the surface of the mineral reflects light like glass. Pearly luster is important in identifying the feldspars, which are the most common type of mineral. Pearly luster refers to a subtle irridescence or color play in the reflected light, same way pearls reflect light.
Silky means relecting light with a silk-like sheen. Greasy luster looks similar to the luster of solidified bacon grease.
Minerals with dull luster reflect very little light. Identifying luster takes a little practice. Remember to distinguish luster from color. Figure 4. Figure 5. The streak of hematite across an unglazed porcelain plate is red-brown. Streak is a more reliable property than color because streak does not vary. Minerals that are the same color may have a different colored streak.
Many minerals, such as the quartz in the Figure 3, do not have streak. To check streak, scrape the mineral across an unglazed porcelain plate Figure 5.
Yellow-gold pyrite has a blackish streak, another indicator that pyrite is not gold, which has a golden yellow streak. Mass is a measure of the amount of matter in an object. The amount of space an object takes up is described by its volume. The density of an object depends on its mass and its volume. For example, the water in a drinking glass has the same density as the water in the same volume of a swimming pool. The specific gravity of a substance compares its density to that of water.
Substances that are more dense have higher specific gravity. Hardness is the strength with which a mineral resists its surface being scraped or punctured.
In working with hand samples without specialized tools, mineral hardness is specified by the Mohs hardness scale. The Mohs hardness scale is based 10 reference minerals, from talc the softest Mohs hardness of 1 , to diamond the hardest Mohs hardness of It is a relative, or nonlinear, scale. A hardness of 2.
A metallic luster is shiny and similar to the reflection from a metal object, such as a faucet. Lustre British English or luster American English; see spelling differences is the way light interacts with the surface of a crystal, rock, or mineral. A range of terms are used to describe lustre , such as earthy, metallic, greasy, and silky.
What is the softest mineral? What is a mineral made of? Minerals are the building blocks of rocks. They are non-living, solid, and, like all matter, are made of atoms of elements. There are many different types of minerals and each type is made of particular groups of atoms. The atoms are arranged in a network called a crystal lattice. What is the hardest mineral?
What are the properties of minerals? The following physical properties of minerals can be easily used to identify a mineral: Color. Cleavage or Fracture. Crystalline Structure. Diaphaneity or Amount of Transparency. What determines a minerals hardness? Hardness is measured by the resistance which a smooth surface offers to abrasion. The degree of hardness is determined by observing the comparative ease or difficulty which which one mineral is scratched by another.
Table showing Mohs' relative hardness scale. Mohs' original hardness values are highlighted in yellow. Is luster physical or chemical? The Physical and Chemical Properties of a substance enable chemists to understand how it will behave under various conditions.
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