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Questions and Answers
What does the term 'Euhedral' refer to in mineralogy?
Which mineral displays radial or stellate crystal habits?
What is a characteristic of fibrous minerals?
Which of the following colors is extremely rare in garnets?
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What type of minerals are likely to be found in smaller quantities within rocks?
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What defines the hardness of a mineral?
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Which mineral is NOT associated with a fibrous structure?
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Which mineral is unlikely to be found in aluminium-poor rocks like quartzite?
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What is the primary reason for not relying on color alone for mineral identification?
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Which of the following minerals forms acicular habits?
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What describes an aggregate in mineralogy?
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What is a key consideration when identifying minerals based on physical properties?
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Which crystal habit is characterized by long, slender prisms?
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What makes color an unreliable property for mineral identification?
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Which of the following minerals exhibits an octahedral habit?
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What type of crystal habit is described as grape-like masses?
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What mineral is primarily associated with the term 'Horneblendite'?
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What is the typical appearance of Biotite crystals?
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Which mineral is commonly sold under the name 'black granite'?
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What is the primary reason for the typical dark color of Hornblende minerals?
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What type of optical properties can Biotite exhibit?
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Who is Biotite named after?
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In what form can Biotite crystals be found?
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Which of the following describes Biotite's occurrence in collections?
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What is the specific gravity range of Biotite?
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Which property indicates that Biotite has a tendency to break into thin sheets or flakes?
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What is the classic chemical formula for Biotite?
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Which of the following minerals is NOT considered an individual member of the Biotite group?
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In what type of rock is Biotite especially noted?
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Which individual member of Biotite is manganese-rich?
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What is the general color range of Biotite?
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What feature describes the appearance of Biotite crystals?
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What is the primary chemical formula for calcite?
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Which of the following colors is NOT associated with calcite?
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What property of calcite is characterized by the ability to bend light?
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Which calcite variety is characterized by a crumbly white appearance?
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What is the crystal system of calcite?
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What type of structures can calcite be utilized for?
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Which calcite variety is known for its dark color and bitumen inclusions?
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How does flowstone calcite typically form?
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Study Notes
Rock-Forming Minerals
- Andalusite is a rock-forming mineral with the chemical formula Al₂SiO₅ and is unlikely to be found in rocks with low aluminum content like quartzite.
- The composition of magma determines the types of minerals that form during igneous processes.
- Minerals can be identified based on their physical properties, but some require a petrographic microscope or complex analytical techniques for accurate identification.
- It is best to use multiple diagnostic criteria to identify a mineral, and a hand lens can help to improve clarity.
Accessory Minerals
- Accessory minerals occur in rocks in small quantities.
- They can provide valuable information about the geological history of the rock, such as the rock's age.
- Examples of accessory minerals include:
- Garnet
- Corundum
Physical Properties of Minerals
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Color is one of the most noticeable features of a mineral, but it is often unreliable for identification.
- Corundum (Al₂O₃) can form as ruby (red due to chromium) or sapphire (commonly blue, but also found in yellow, orange, pink, green, and brown).
- Garnets can exhibit a wide range of colors depending on their composition and can be found in virtually any color, with blue being extremely rare.
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Crystal Habit refers to the characteristic shape of a mineral's crystal or crystal aggregate.
- Euhedral: Crystals with well-developed faces (e.g. garnet crystals).
- Aggregates: Minerals that appear as groups or masses of crystals rather than individual, well-defined crystals (e.g., asbestosis usually found as an aggregate of very fine fibers).
- Hardness is a measure of how resistant a mineral is to scratching and is controlled by the chemical composition and structure of the mineral.
- Transparency can be used to identify minerals and is described as transparent, translucent, or opaque.
- Specific Gravity is the ratio of the mineral's density to the density of water.
- Luster describes how light reflects off the surface of the mineral and can be metallic, glassy, pearly, or dull.
- Cleavage refers to the tendency of a mineral to break along smooth, flat surfaces.
- Fracture describes the way a mineral breaks when it is not cleaved.
- Tenacity describes a mineral's resistance to deformation.
- Other Identification Marks can help to distinguish certain minerals (e.g., the tendency for small pieces or flakes of biotite to peel off).
Mineral Identification Using Crystal Habits
- Acicular: Needle-like, e.g., natrolite, rutile.
- Granular: Aggregates of crystals, e.g., bornite, scheelite.
- Bladed: Blade-like, slender, and flattened, e.g., kyanite.
- Hexagonal: Six-sided, e.g., quartz, hanksite.
- Botryoidal: Grape-like masses, e.g., malachite.
- Massive: No distinct shape, e.g., hematite, turquoise, realgar.
- Columnar: Long, slender prisms, e.g., calcite, gypsum.
- Octahedral: Eight-sided, e.g., diamond, magnetite.
- Cubic: Cube-shaped, e.g., pyrite, galena, wulfenite.
- Platy: Flat, tablet-like shape, e.g., halite.
- Dendritic: Tree-like, branching in multiple directions, e.g., pyrolusite, native copper, native silver.
- Prismatic: Elongate, prism-like, e.g., tourmaline, beryl.
- Fibrous: Very slender prisms, e.g., asbestos, tremolite.
- Radial or Stellate: Radiating outwards from a central point, star-like, e.g., wavellite, pyrophyllite.
- Foliated or Lamellar: Layered structure, parts easily split into very thin sheets, e.g., muscovite, biotite.
Hornblende
- A major constituent of the earth and extremely common.
- It is a rock-forming mineral and forms its own rock type known as Horneblendite, a dark rock formed mostly from hornblende.
- Hornblende's typical dark color and opacity are usually caused by iron in its structure.
- It is used to estimate the depth of crystallization of plutonic rocks.
- Important for understanding the crystallization of magma and useful for mineral exploration.
Biotite
- A very common form of mica.
- Named in honor of Jean Baptiste Biot (1774-1862), a French physicist, mathematician, and astronomer who researched the mica minerals for their optical properties.
- It is usually lacking in collections except as an accessory mineral to other minerals.
- It can come in enormous crystal sheets weighing several hundred pounds or in thin sheets.
- Difficult to clean as it absorbs water internally and breaks apart.
- In 1998, Biotite was removed as an individual mineral species by the IMA and instead declared as a group name for the following individual members:
- Phlogopite
- Annite
- Siderophyllite
- Eastonite
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Physical Properties:
- Chemical formula: K(Mg,Fe2+3)(Al,Fe3+)Si3O10(OH,F)2
- Composition: Basic fluoro potassium, magnesium, iron aluminum silicate
- Color: Black, dark brown, dark green, reddish black. Individual group members such as Phlogopite and Eastonite can be in lighter colors.
- Transparency: Translucent to opaque.
- Specific Gravity: 2.8 – 3.4
- Luster: Pearly
- Cleavage: 1, 1
- Fracture: Uneven
- Tenacity: Sectile, elastic
- Other ID Marks: Tendency for small pieces or flakes or peel off
- Group: Silicates; Phyllosilicates; Mica Group
- Striking Features: Flaky habit, crystals, sectility, and mode of occurrence
- Environment: Common rock-forming mineral. It is especially noted in metamorphic rocks. It is also found in igneous rock and the primary mica in rare earth pegmatites.
- Rock Type: Igneous, Metamorphic
- Popularity: 2
- Prevalence: 1
- Demand: 2
- Varieties: Manganophyllite - manganese-rich.
Muscovite
- Most common mineral of the mica family.
- An important rock-forming mineral present in igneous, metamorphic, and sedimentary rocks.
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Physical Properties:
- Composition: Basic fluoro potassium, aluminum, silicate
- Color: Colorless to silver gray, or pale tan.
- Hardness: 2-2.5
- Cleavage: Perfect, one direction
- Luster: Pearly to vitreous, translucent, silvery
- Streak: White or faintly colorless
- Specific Gravity: 2.8-3.1
- Fracture: Uneven, conchoidal
- Tenacity: Brittle, elastic
- Other ID Marks: Thin sheets peel apart easily
- Group: Silicates; phyllosilicates; mica group
- Environment: Common in Igneous, metamorphic and sedimentary rocks. Often used as a building material because it is strong and flexible and does not react chemically with other materials.
- Popularity: 1
- Prevalence: 1
- Demand: 1
Calcite
- A widely used material in construction and industry.
- Metamorphic rocks have served as dimension stones and mortar for thousands of years, notably in the pyramids of Egypt and Latin America.
- Rough and polished limestone and marble are essential in prestigious architecture.
- Calcite is crucial for producing cement and concrete, which are easily mixed and transported.
- Concrete is utilized for buildings, highways, bridges, walls, and various structures.
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Physical Properties:
- Chemical formula: CaCO3
- Composition: Calcium carbonate, sometimes with impurities of iron, magnesium, or manganese, and occasionally zinc and cobalt.
- Variable formula: (Ca,Fe,Mg,Mn,Zn,Co)CO3
- Color: Colorless, white, yellow, brown, orange, pink, red, purple, blue, green, gray, black, may also be multicolored or banded.
- Streak: White
- Hardness: 3
- Crystal system: Hexagonal
- Crystal forms and Aggregates: Occurs in a great variety of shapes, with the most common forms as rhombohedral and scalenohedral crystals. Crystals may be tabular, acicular, prismatic, flaky, and needle-like. May occur as bundles of scalenohedrons, intergrown.
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Varieties:
- Agaric Mineral: Crumbly white calcite found on cavern floors near stalagmites and stalactites.
- Anthraconite: Dark gray to black variety of calcite with bitumen coating or inclusions.
- Cobaltocalcite: Refers to an intermediary mineral between Calcite and Sphaerocobaltite in a solid solution.
- Dogtooth Calcite: Calcite in groupings of thick and pointy scalenohedral crystals.
- Flowstone: Calcite formed by mineral-rich water that deposits the dissolved mineral on the walls of caverns and cliffs, forming a smooth and humpy growth.
- Iceland Spar: Large, transparent, colorless to lightly colored, rhombohedral variety of Calcite. Double refraction is especially noted in Iceland Spar crystals.
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Description
Explore the fascinating world of rock-forming and accessory minerals in this quiz. Learn about their chemical compositions, identification methods, and the geological significance of these minerals. Test your knowledge on physical properties and the role of minerals in understanding rock formation.
