what is the most reliable clue to a minerals identity
Lesson Objectives
- Explain how minerals are identified.
- Depict how color, luster, and streak are used to identify minerals.
- Explain how the hardness of a mineral is measured.
- Identify boosted properties that can be used to identify some minerals.
Vocabulary
- cleavage
- fracture
- hardness
- luster
- mineralogist
- streak
Introduction
Minerals tin be identified by their physical characteristics. The physical properties of minerals are related to their chemical composition and bonding. Some characteristics, such as a mineral's hardness, are more useful for mineral identification. Colour is readily appreciable and certainly obvious, just it is commonly less reliable than other physical properties.
How are Minerals Identified?
Mineralogists are scientists who written report minerals. One of the things mineralogists must practise is identify and categorize minerals. While a mineralogist might utilise a loftier-powered microscope to place some minerals, most are recognizable using physical properties.
Cheque out the mineral inEffigy below. What is the mineral's color? What is its shape? Are the individual crystals shiny or tiresome? Are in that location lines (striations) running across the minerals? In this lesson, the properties used to identify minerals are described in more than detail.
This mineral has shiny, aureate, cubic crystals with striations, and so it is pyrite.
Color, Streak, and Luster
Diamonds are popular gemstones because the fashion they reverberate calorie-free makes them very sparkly. Turquoise is prized for its striking greenish-bluish color. Notice that specific terms are being used to describe the appearance of minerals.
Color
Color is rarely very useful for identifying a mineral. Unlike minerals may be the same colour. Real gold, as seen inEffigy below, is very similar in color to the pyrite inEffigy higher up.
This mineral is shiny, very soft, heavy, and aureate in color, and is really gold.
The aforementioned mineral may too exist found in different colors.Figure below shows i sample of quartz that is colorless and another quartz that is purple. A tiny amount of iron makes the quartz majestic. Many minerals are colored by chemical impurities.
Purple quartz, known as amethyst, and clear quartz are the same mineral despite the different colors.
Streak
Streak is the color of a mineral's powder. Streak is a more reliable property than color because streak does not vary. Minerals that are the same color may accept a different colored streak. Many minerals, such as the quartz in theFigure above, do not take streak.
To check streak, scrape the mineral across an unglazed porcelain plate (Figure beneath). Xanthous-gold pyrite has a blackish streak, another indicator that pyrite is not gold, which has a golden yellow streak.
The streak of hematite across an unglazed porcelain plate is red-brown.
Luster
Luster describes the reflection of calorie-free off a mineral's surface. Mineralogists have special terms to depict luster. One simple way to allocate luster is based on whether the mineral is metallic or non-metal. Minerals that are opaque and shiny, such as pyrite, accept a metallic luster. Minerals such as quartz take a non-metal luster. Different types of not-metal luster are described inTable below.
| Luster | Advent |
|---|---|
| Adamantine | Sparkly |
| Earthy | Boring, dirt-like |
| Pearly | Pearl-like |
| Resinous | Like resins, such every bit tree sap |
| Silky | Soft-looking with long fibers |
| Vitreous | Glassy |
Can you match the minerals inFigure below with the correct luster fromTable higher up?
(a) Diamond has an adamantine luster. (b) Quartz is not sparkly and has a vitreous, or burnished, luster. (b) Sulfur reflects less low-cal than quartz, so information technology has a resinous luster.
Hardness
Hardness is a measure of whether a mineral will scratch or exist scratched. Mohs Hardness Scale, shown inTable below, is a reference for mineral hardness.
| Hardness | Mineral |
|---|---|
| i | Talc |
| 2 | Gypsum |
| 3 | Calcite |
| 4 | Fluorite |
| 5 | Apatite |
| 6 | Feldspar |
| 7 | Quartz |
| viii | Topaz |
| 9 | Corundum |
| 10 | Diamond |
With a Mohs scale, anyone can test an unknown mineral for its hardness. Imagine you have an unknown mineral. Y'all find that it tin can scratch fluorite or fifty-fifty apatite, but feldspar scratches it. You know so that the mineral'due south hardness is between five and half dozen. Note that no other mineral can scratch diamond.
Cleavage and Fracture
Breaking a mineral breaks its chemical bonds. Since some bonds are weaker than other bonds, each type of mineral is likely to intermission where the bonds between the atoms are weaker. For that reason, minerals suspension apart in characteristic means.
Cleavage is the tendency of a mineral to interruption along sure planes to make smooth surfaces. Halite breaks between layers of sodium and chlorine to class cubes with smooth surfaces (Figure below).
A close-upwardly view of sodium chloride in a water bubble aboard the International Infinite Station.
Mica has cleavage in i direction and forms sheets (Figure beneath).
Sheets of mica.
Minerals can cleave into polygons. Fluorite forms octahedrons (Figure beneath).
This rough diamond shows its octahedral cleavage.
Ane reason gemstones are beautiful is that the cleavage planes brand an attractive crystal shape with smooth faces.
Fracture is a pause in a mineral that is not forth a cleavage airplane. Fracture is non always the same in the aforementioned mineral because fracture is not determined by the construction of the mineral.
Minerals may take characteristic fractures (Figure below). Metals unremarkably fracture into jagged edges. If a mineral splinters like forest, it may be fibrous. Some minerals, such every bit quartz, form smooth curved surfaces when they fracture.
Chrysotile has splintery fracture.
Other Identifying Characteristics
Some minerals accept other unique properties, some of which are listed inTabular array beneath. Tin can yous name a unique property that would allow you to instantly identify a mineral that's been described quite a bit in this affiliate? (Hint: It is almost likely found on your dinner table.)
| Property | Clarification | Example of Mineral |
|---|---|---|
| Fluorescence | Mineral glows under ultraviolet light | Fluorite |
| Magnetism | Mineral is attracted to a magnet | Magnetite |
| Radioactivity | Mineral gives off radiation that can be measured with Geiger counter | Uraninite |
| Reactivity | Bubbles form when mineral is exposed to a weak acid | Calcite |
| Smell | Some minerals have a distinctive smell | Sulfur (smells like rotten eggs) |
| Taste | Some minerals gustatory modality salty | Halite |
A simple lesson on how to identify minerals is seen in this video: http://www.youtube.com/picket?v=JeFVwqBuYl4.
Lesson Summary
- Minerals have distinctive properties that can be used to help identify them.
- Color and luster describe the mineral's outer advent. Streak is the color of the pulverisation.
- Mohs Hardness Calibration is used to compare the hardness of minerals.
- Cleavage or the feature way a mineral breaks depends on the crystal structure of the mineral.
- Some minerals have special backdrop that can be used to aid identify them.
Review Questions
- Which properties of a mineral describe the way it breaks apart?
- A mineral looks dry and chalky. What sort of luster does it have?
- What causes a mineral to have the properties that it has?
- Apatite scratches the surface of an unknown mineral. Which mineral would yous use next to test the mineral's hardness — fluorite or feldspar? Explicate your reasoning.
- Why is streak more than reliable than color when identifying a mineral?
- Mineral A has a density of five g/cm3. Mineral B is twice equally dense as Mineral A. What is the density of Mineral B?
- Why exercise some minerals cleave along certain planes?
Further Reading / Supplemental Links
- Mineral Color: http://geology.csupomona.edu/alert/mineral/colour.htm/
- Physical Characteristics of Minerals: http://world wide web.galleries.com/minerals/physical.htm.
- Mineral Identification: http://geology.csupomona.edu/warning/mineral/minerals.htm.
Points to Consider
- If a mineral is magnetic, do you know for certain what mineral it is?
- Some minerals are colored because they contain chemical impurities. How did the impurities become into the mineral?
- What two properties of a mineral sample would y'all have to mensurate to summate its density?
- How much exercise minerals reflect the surround in which they formed?
Source: https://courses.lumenlearning.com/earthscience/chapter/mineral-identification/
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