what are the eight properties of mineral that can be used to identify minerals

What are Minerals?

All rocks except obsidian and coal are made of minerals. (Obsidian is a volcanic rock made of glass and coal is fabricated of organic carbon.) Almost rocks incorporate several minerals in a mixture characteristic of the particular stone type. When identifying a stone you must start identify the individual minerals that make upwardly that rock.

Minerals are naturally occurring, inorganic solids with a definite chemical limerick and a crystal lattice structure. Although thousands of minerals in the earth have been identified, just ten minerals make upwards most of the volume of the world's crust—plagioclase, quartz, orthoclase, amphibole, pyroxene, olivine, calcite, biotite, garnet, and clay.

Together, the chemical formula (the types and proportions of the chemic elements) and the crystal lattice (the geometry of how the atoms are arranged and bonded together) make up one's mind the physical properties of minerals.

The chemical formula and crystal lattice of a mineral tin can only be determined in a laboratory, but by examining a mineral and determining several of its physical properties, you can place the mineral. Start, you lot need to become familiar with the physical properties of minerals and how to recognize them.

Minerals can be identified by their physical characteristics. The concrete properties of minerals are related to their chemical limerick and bonding. Some characteristics, such as a mineral'south hardness, are more useful for mineral identification. Color is readily observable and certainly obvious, but it is usually less reliable than other physical properties.

How are Minerals Identified?

Figure i. This mineral has shiny, gold, cubic crystals with striations, so information technology is pyrite.

Mineralogists are scientists who written report minerals. Ane of the things mineralogists must do is identify and categorize minerals. While a mineralogist might utilise a loftier-powered microscope to identify some minerals, most are recognizable using physical properties.

Check out the mineral in figure 1. What is the mineral's color? What is its shape? Are the individual crystals shiny or deadening? Are there lines (striations) running beyond the minerals?

Colour, Streak, and Luster

Diamonds are popular gemstones because the style they reverberate light makes them very sparkly. Turquoise is prized for its hitting greenish-blue color. Detect that specific terms are being used to describe the appearance of minerals.

Color

Figure 2. This mineral is shiny, very soft, heavy, and gold in color, and is really golden.

Color is often useful, simply should not be relied upon. Different minerals may be the same color. Real gold, equally seen in figure 2, is very similar in color to the pyrite in figure ane.

Additionally, Some minerals come in many different colors. Quartz, for case, may exist clear, white, gray, brownish, yellow, pinkish, cerise, or orangish. So color tin can help, only do not rely on colour as the determining property. Figure 3 shows ane sample of quartz that is colorless and another quartz that is purple. A tiny amount of fe makes the quartz purple. Many minerals are colored past chemic impurities.

Figure 3. Regal quartz, known every bit amethyst, and articulate quartz are the same mineral despite the different colors.

Luster

Luster describes the reflection of light off a mineral'south surface. Mineralogists have special terms to describe luster. 1 simple way to classify luster is based on whether the mineral is metallic or non-metallic. Minerals that are opaque and shiny, such equally pyrite, take a metal luster. Minerals such equally quartz have a non-metallic luster.

Luster is how the surface of a mineral reflects calorie-free. It is not the same thing as color, and then it crucial to distinguish luster from color. For example, a mineral described equally "shiny yellow" is being described in terms of luster ("shiny") and colour ("yellow"), which are two unlike physical properties. Standard names for luster include metallic, glassy, pearly, silky, greasy, and dull. It is often useful to first decide 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 equally do many other minerals. Of the nonmetallic lusters, glassy is the most common and means the surface of the mineral reflects calorie-free like glass. Pearly luster is important in identifying the feldspars, which are the nigh common blazon of mineral. Pearly luster refers to a subtle irridescence or colour play in the reflected low-cal, same fashion 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 do. Remember to distinguish luster from color.

Different types of not-metallic luster are described in tabular array i.

Table 1. Six types of non-metallic luster.
Luster	Appearance
Adamantine	Sparkly
Earthy	Dull, dirt-like
Pearly	Pearl-like
Resinous	Like resins, such every bit tree sap
Silky	Soft-looking with long fibers
Vitreous	Glassy

Tin can you match the minerals in figure iv with the right luster from table 1?

Figure 4. (a) Diamond has an adamantine luster. (b) Quartz is not sparkly and has a vitreous, or glassy, luster. (c) Sulfur reflects less light than quartz, and so it has a resinous luster.

Streak

Figure 5. The streak of hematite across an unglazed porcelain plate is red-brownish.

Streak is the color of a mineral's powder. Streak is a more than reliable property than color because streak does non vary. Minerals that are the same colour may take a dissimilar colored streak. Many minerals, such as the quartz in the figure 3, do not have streak.

To cheque streak, scrape the mineral across an unglazed porcelain plate (Figure five). Yellow-gilt pyrite has a blackish streak, another indicator that pyrite is not gold, which has a golden yellow streak.

Specific Gravity

Density describes how much matter is in a certain amount of infinite: density = mass/volume.

Mass is a measure out of the corporeality of matter in an object. The amount of space an object takes up is described past its book. The density of an object depends on its mass and its volume. For example, the water in a drinking glass has the aforementioned density as the water in the same volume of a swimming puddle.

The specific gravity of a substance compares its density to that of h2o. Substances that are more dense accept higher specific gravity.

Hardness

Hardness is the force 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 x reference minerals, from talc the softest (Mohs hardness of 1), to diamond the hardest (Mohs hardness of 10). It is a relative, or nonlinear, scale. A hardness of 2.5 simply means that the mineral is harder than gypsum (Mohs hardness of 2) and softer than calcite (Mohs hardness of 3). To compare the hardness of two minerals see which mineral scratches the surface of the other.

Table ii. Mohs Hardness Scale
Hardness	Index Minerals	Mutual Objects
1	talc
2	gypsum	2.5-fingernail
three	calcite	3.5-pure, untarnished copper
4	fluorite
5	feldspar	5 to 5.five-stainless steel
		v.5 to half-dozen-glass
6	apatite	6 to 6.v-hard steel file
7	quartz
eight	topaz
ix	corundum
10	diamond

With a Mohs scale, anyone tin test an unknown mineral for its hardness. Imagine you have an unknown mineral. You find that information technology tin scratch fluorite or even feldspar, but apatite scratches it. You know then that the mineral's hardness is between 5 and 6. Notation that no other mineral can scratch diamond.

Cleavage and Fracture

Breaking a mineral breaks its chemic bonds. Since some bonds are weaker than other bonds, each type of mineral is likely to break where the bonds between the atoms are weaker. For that reason, minerals interruption apart in characteristic means.

Cleavage

Figure 6. A close-upwardly view of sodium chloride in a water chimera aboard the International Space Station.

Cleavage is the tendency of a mineral to break along sure planes to make shine surfaces. Halite breaks between layers of sodium and chlorine to form cubes with smooth surfaces (figure 6).

A mineral that naturally breaks into perfectly flat surfaces is exhibiting cleavage. Not all minerals have cleavage. A cleavage represents a direction of weakness in the crystal lattice. Cleavage surfaces can be distinguished by how they consistently reverberate calorie-free, as if polished, smooth, and even. The cleavage properties of a mineral are described in terms of the number of cleavages and, if more than one cleavage, the angles between the cleavages. The number of cleavages is the number or directions in which the mineral cleaves. A mineral may showroom 100 cleavage surfaces parallel to each other. Those stand for a single cleavage because the surfaces are all oriented in the same diretion. The possible number of cleavages a mineral may have are one,2,3,four, or 6. If more than than one cleavage is nowadays, and a device for measuring angles is not available, simply land whether the cleavages intersect at ninety° or non 90°.

To meet mineral cleavage, hold the mineral up beneath a stiff light and motion it around, move it around some more, to see how the different sides reflect lite. A cleavage direction will show upward as a polish, shiny, evenly bright sheen of lite reflected past 1 ready of parallel surfaces on the mineral.

Mica has cleavage in one direction and forms sheets (figure 7).

Figure 7. Sheets of mica.

Effigy eight. This rough diamond shows its octahedral cleavage.

Minerals can cleave into polygons. Fluorite forms octahedrons (figure eight).

Ane reason gemstones are beautiful is that the cleavage planes make an attractive crystal shape with shine faces.

Fracture

Fracture is a break in a mineral that is not along a cleavage plane. Fracture is not always the same in the same mineral because fracture is not determined by the structure of the mineral.

Minerals may have feature fractures (figure 9). Metals usually fracture into jagged edges. If a mineral splinters similar wood, it may exist fibrous. Some minerals, such every bit quartz, form smooth curved surfaces when they fracture.

Effigy 9. Chrysotile has splintery fracture.

All minerals have fracture. Fracture is breakage, which occurs in directions that are not cleavage directions. Some minerals, such as quartz, have no cleavage whatever. When a mineral with no cleavage is broken autonomously by a hammer, information technology fractures in all directions. Quartz is said to exhibit conchoidal fracture. Conchoidal fracture is the style a thick slice of drinking glass breaks with concentric, curving ridges on the broken surfaces. However, some quartz crystals have so many flaws that instead of exhibiting conchoidal fracture they simply showroom irregular fracture. Irregular fracture is a standard term for fractures that do non showroom whatsoever of the qualities of the other fracture types. In introductory geology, the key fracture types to remember are irregular, which nearly minerals showroom, and conchoidal, seen in quartz.

Crystal Shape

All minerals are crystalline, but but some have the opportunity to exhibit the shapes of their crystals, their crystal forms. Many minerals in an introductory geology lab do not exhibit their crystal form. If a mineral has space while it grows, it may form natural crystals, with a crystal shape reflecting the geometry of the mineral's internal crystal lattice. The shape of a crystal follows the symmetry of its crystal lattice. Quartz, for example, forms six-sided crystals, showing the hexagonal symmetry of its crystal lattice. There are two complicating factors to call back here: (ane) minerals do not e'er form overnice crystals when they grow, and (2) a crystal face is different from a cleavage surface. A crystal face forms during the growth of the mineral. A cleavage surface is formed when the mineral is broken.

Other Identifying Characteristics

There are some backdrop that only help to distinguish a small number of minerals, or fifty-fifty merely a single mineral. An case of such a special holding is the effervescent reaction of calcite to a weak solution of muriatic acid (5% HCl). Calcite fizzes or effervesces equally the HCl solution dissolves it and creates CO₂ gas. Calcite is easy to identify fifty-fifty without testing the reaction to HCl, by its hardness, luster and cleavage.

Some other special holding is magnetism. This can be tested by seeing if a small-scale magnet responds to the mineral. The most common mineral that is strongly magnetic is the mineral magnetite. A special holding that shows up in some sample of plagioclase feldspar is its tendency to exhibit striations on cleavage surfaces. Striations are perfectly straight, fine, parallel lines. Magnification may be required to see striations on plagioclase cleavage surfaces. Other special properties may be encountered on a mineral to mineral basis.

Some minerals have other unique properties, some of which are listed in tabular array 3. Can yous proper name a unique holding that would let you to instantly identify a mineral that'south been described quite a flake in this chapter? (Hint: It is about likely found on your dinner table.)

Table iii. Some minerals take unusual backdrop that tin be used for identification.
Property	Description	Example of Mineral
Fluorescence	Mineral glows nether ultraviolet calorie-free	Fluorite
Magnetism	Mineral is attracted to a magnet	Magnetite
Radioactivity	Mineral gives off radiation that can exist measured with Geiger counter	Uraninite
Reactivity	Bubbling course when mineral is exposed to a weak acid	Calcite
Smell	Some minerals have a distinctive smell	Sulfur (smells like rotten eggs)
Taste	Some minerals taste salty	Halite

Contribute!

Did you accept an idea for improving this content? We'd love your input.

Better this pageLearn More

williamsarrierld.blogspot.com

Source: https://courses.lumenlearning.com/geo/chapter/reading-physical-characteristics-of-minerals/

Share this post