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Questions and Answers
What is the term for the property of a mineral that allows light to pass through completely?
What is the term for the property of a mineral that allows light to pass through completely?
- Opaque
- Fluorescent
- Transparent (correct)
- Translucent
All minerals are opaque.
All minerals are opaque.
False (B)
Name one factor responsible for the color in minerals.
Name one factor responsible for the color in minerals.
Presence of a color-causing element (chromophore)
The scale that measures the hardness of minerals is called _______.
The scale that measures the hardness of minerals is called _______.
Which of the following is NOT a physical property of minerals?
Which of the following is NOT a physical property of minerals?
Match the following types of transparency with their definitions:
Match the following types of transparency with their definitions:
What mineral property indicates how a mineral breaks along flat planes?
What mineral property indicates how a mineral breaks along flat planes?
A mineral that appears red due to the presence of _______ would be exhibiting a color-causing element.
A mineral that appears red due to the presence of _______ would be exhibiting a color-causing element.
What is the phenomenon called when a mineral appears different in colors or color intensities depending on its crystallographic orientation?
What is the phenomenon called when a mineral appears different in colors or color intensities depending on its crystallographic orientation?
Pleochroism is solely determined by the impurities present in a mineral.
Pleochroism is solely determined by the impurities present in a mineral.
What optical effect is observed in labradorite and plagioclase due to thin film interference?
What optical effect is observed in labradorite and plagioclase due to thin film interference?
The luster that sparkles like a diamond, characterized by a high refractive index, is known as __________.
The luster that sparkles like a diamond, characterized by a high refractive index, is known as __________.
Match the following materials with their corresponding features:
Match the following materials with their corresponding features:
What causes the color in transition metals?
What causes the color in transition metals?
Electrons cannot be excited by energy in the visible spectrum in transition metals.
Electrons cannot be excited by energy in the visible spectrum in transition metals.
What effect can result from the transfer of electrons between O2- and metal cations?
What effect can result from the transfer of electrons between O2- and metal cations?
Color centers are caused by structural defects from a missing ________.
Color centers are caused by structural defects from a missing ________.
Match the following minerals with their respective colors:
Match the following minerals with their respective colors:
What is the essential element that causes a green color in olivine at lower concentrations?
What is the essential element that causes a green color in olivine at lower concentrations?
Structural defects in minerals can lead to variations in color due to missing ions.
Structural defects in minerals can lead to variations in color due to missing ions.
What are the end-member formulas for Forsterite and Fayalite?
What are the end-member formulas for Forsterite and Fayalite?
What type of cleavage occurs perpendicular to the c axis of a crystal?
What type of cleavage occurs perpendicular to the c axis of a crystal?
Cleavage is always present in all minerals.
Cleavage is always present in all minerals.
What are the two angles typically associated with the cleavage of pyroxenes and amphiboles?
What are the two angles typically associated with the cleavage of pyroxenes and amphiboles?
Cleavage can be described as __________, __________, and __________.
Cleavage can be described as __________, __________, and __________.
Which type of cleavage is typical in minerals like mica?
Which type of cleavage is typical in minerals like mica?
Match the type of cleavage with its respective example:
Match the type of cleavage with its respective example:
Parting is a type of cleavage that can occur in minerals.
Parting is a type of cleavage that can occur in minerals.
Why is cleavage important in mineralogy?
Why is cleavage important in mineralogy?
What method is used to detect minerals containing highly radioactive elements?
What method is used to detect minerals containing highly radioactive elements?
Fluorescence is not used in the automated processing of rubies.
Fluorescence is not used in the automated processing of rubies.
What is the texture typical of microcline or orthoclase that displays exsolution?
What is the texture typical of microcline or orthoclase that displays exsolution?
Minerals such as __________, __________, and __________ feel greasy to the touch.
Minerals such as __________, __________, and __________ feel greasy to the touch.
Which mineral can be identified by its smell when broken due to weathering?
Which mineral can be identified by its smell when broken due to weathering?
Match the following minerals to their distinct characteristics:
Match the following minerals to their distinct characteristics:
Tasting minerals is generally considered safe.
Tasting minerals is generally considered safe.
What is the advanced stage used for identification when physical properties do not provide sufficient information?
What is the advanced stage used for identification when physical properties do not provide sufficient information?
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Study Notes
Physical Properties of Minerals
- Color is caused by the selective absorption of certain wavelengths of visible light.
- The main factors responsible for color in minerals:
- Presence of a color-causing element (chromophore) that is essential to the mineral composition
- Presence of a minor color-causing element (chromophore)
- Crystal structure
- Crystal structure defects
- Inclusions of very fine impurities of another mineral or substance
- Directional optical effects caused by thin-film interference
- Color can be caused by crystal field transitions:
- Transition metals have partly filled inner 3d orbitals
- Electrons in these orbitals can be excited by energy in the visible spectrum, resulting in the absorption of specific wavelengths of light.
- Color can be caused by charge transfers in the mineral structure.
- Color can be caused by color centers, structural defects from a missing ion.
- Color can vary due to the concentration of chromophore elements, as seen in the example of olivine:
- The mineral olivine (Forsterite-Fayalite series) contains Fe2+ which causes green color in lower concentrations, and dark brown in higher concentrations.
- Pleochroism refers to the phenomenon of different colors or color intensities being observed in a mineral when viewed at different crystallographic orientations
- Olivine is a common mantle mineral with a typical formula of ~ Mg1.6Fe0.4SiO4.
- "End-member" Forsterite (Mg2SiO4) and "End-member" Fayalite (Fe2SiO4) are the two extremes of the olivine series.
- Color can be caused by impurities: nano to micro-scale particle inclusions of a different material
- Color can be caused by optical effects like thin film interference in labradorite and "peristerite" plagioclase.
- The luster of a mineral describes the interaction of light on its surface.
- Luster is affected by the crystallinity and refractive index of the mineral.
- Some common descriptive terms for luster include:
- Adamantine: sparkles like diamond - high refractive index.
- Vitreous: glass-like
- Resinous: resin-like
- Pearlescent: pearl-like
- Metallic: metallic appearance
- Cleavage is the tendency of a mineral to break along planes of weak bonding.
- Cleavage is regular and reproducible and parallel to actual or possible crystal faces.
- Cleavage can be described in terms of how easily it is produced:
- Perfect
- Imperfect
- Good
- Distinct
- Indistinct
- Poor
- Basal cleavage occurs perpendicular to the c axis of a crystal, common in sheet silicates like mica.
- Prismatic cleavage occurs parallel to the c axis of a crystal, typical in amphiboles and pyroxenes.
- Multiple cleavages can produce geometric polygons:
- Octahedral cleavage (e.g., fluorite)
- Cubic cleavage (e.g., halite)
- Rhombohedral cleavage (e.g., calcite, dolomite, siderite).
- Cleavage is crucial for differentiating between similar mineral groups, like pyroxenes and amphiboles.
- Pyroxenes have ~ 90 degree cleavage.
- Amphiboles have ~ 60/120 degree cleavage.
- Parting is NOT cleavage. It is a specific type of breakage along planes in a mineral caused by twinning, exsolution lamellae, structural defects, or chemical alteration.
- Fluorescence is the emission of light by a mineral when it is exposed to ultraviolet (UV) or X-ray radiation.
- Fluorescence has been used in automated ore processing of rubies and diamonds.
- Radioactive minerals containing highly radioactive elements (U, Th) can be detected using scintillometers or geiger counters.
- Exsolutions are mixtures of minerals that formed from the separation of a single homogeneous phase into two or more solid-solution phases under subsolidus conditions.
- Perthite texture is typical of microcline or orthoclase (both K-feldspars) which have exsolved albitic plagioclase lamellae.
- Some minerals like talc, graphite, and molybdenite feel greasy to the touch due to their softness.
- Sulphides often smell like sulfur when broken, or if they are weathering.
- Halite (NaCl) and sylvite (KCl) have distinctive flavors. However, it is generally not a good idea to taste minerals, especially villiaumite (NaF) which is toxic.
- Advanced analytical methods, such as petrographic thin sections and optical properties, are used to identify minerals when physical properties are not sufficient.
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