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Olivine is fundamentally a magnesium iron silicate mineral, characterized by the general chemical formula (Mg,Fe)₂SiO₄, indicating a solid solution series between its endmembers.
Answer: True
This statement accurately reflects the primary chemical composition and formula of olivine, which belongs to the nesosilicate group and exhibits a solid solution series between its magnesium-rich endmember, forsterite, and its iron-rich endmember, fayalite.
Olivine is classified as a sorosilicate, a structural group defined by paired silicate tetrahedra.
Answer: False
Olivine is correctly classified as a nesosilicate (or orthosilicate), characterized by isolated SiO₄ tetrahedra, not paired tetrahedra as found in sorosilicates.
Forsterite represents the iron-rich endmember of the olivine solid solution series, while fayalite represents the magnesium-rich endmember.
Answer: False
This statement incorrectly identifies the endmembers. Forsterite (Fo) is the magnesium-rich endmember (Mg₂SiO₄), whereas fayalite (Fa) is the iron-rich endmember (Fe₂SiO₄).
The composition of olivine is typically expressed using molar percentages of its endmembers, denoted as Fo for forsterite and Fa for fayalite.
Answer: True
This is the standard convention for describing olivine compositions, where Fo represents the molar percentage of forsterite and Fa represents the molar percentage of fayalite, such as in Fo₇₀Fa₃₀.
Fayalite, the iron-rich endmember of olivine, exhibits a significantly lower melting temperature than forsterite at atmospheric pressure.
Answer: True
Indeed, fayalite melts at approximately 1,200 °C, whereas forsterite possesses a much higher melting point, around 1,900 °C at atmospheric pressure.
Beyond magnesium, iron, silicon, and oxygen, the most commonly incorporated trace elements in olivine are aluminum and calcium.
Answer: False
While olivine can incorporate various trace elements, manganese (Mn) and nickel (Ni) are the elements most commonly found in significant concentrations, rather than aluminum and calcium.
Fayalite, the magnesium endmember, has the chemical formula Mg₂SiO₄.
Answer: False
Fayalite is the iron-rich endmember with the formula Fe₂SiO₄. The magnesium-rich endmember, forsterite, has the formula Mg₂SiO₄.
What is the fundamental chemical classification of olivine?
Answer: A magnesium iron silicate.
Olivine is classified as a magnesium iron silicate, with the general formula (Mg,Fe)₂SiO₄, placing it within the nesosilicate group.
Which structural group does olivine belong to, based on its silicate structure?
Answer: Neso/Orthosilicate
Olivine's structure consists of isolated SiO₄ tetrahedra, classifying it as a nesosilicate or orthosilicate.
In the olivine solid solution series, which mineral represents the magnesium-rich endmember?
Answer: Forsterite
Forsterite (Mg₂SiO₄) is the magnesium-rich endmember of the olivine solid solution series.
How is the composition of an olivine sample typically expressed, for example, as Fo70Fa30?
Answer: Using molar percentages of its endmembers, forsterite and fayalite.
The composition of olivine is commonly quantified using molar percentages of its endmembers, denoted as Fo (forsterite) and Fa (fayalite), such as Fo₇₀Fa₃₀.
Which statement accurately compares the melting points of forsterite and fayalite at atmospheric pressure?
Answer: Fayalite melts at a significantly lower temperature than forsterite.
Fayalite melts around 1,200 °C, whereas forsterite has a much higher melting point, approximately 1,900 °C at atmospheric pressure.
What elements, besides the primary Mg, Fe, Si, and O, are most commonly found in significant concentrations within olivine?
Answer: Manganese and Nickel
While the primary constituents are Mg, Fe, Si, and O, manganese (Mn) and nickel (Ni) are the trace elements most frequently incorporated into olivine in notable concentrations.
What is the chemical formula for fayalite, the iron-rich endmember of olivine?
Answer: Fe2SiO4
Fayalite, the iron-rich endmember of the olivine series, has the chemical formula Fe₂SiO₄.
What is the Strunz classification code for olivine?
Answer: 9.AC.05
In the Strunz classification system, olivine is assigned the code 9.AC.05, reflecting its position within the nesosilicates.
The mineral name 'olivine' is derived from its characteristic metallic luster.
Answer: False
The name 'olivine' is derived from its characteristic olive-green color, not its luster, which is typically vitreous (glassy).
The IMA symbol assigned to olivine is 'Ol'.
Answer: True
The International Mineralogical Association (IMA) has officially designated 'Ol' as the symbol for olivine.
Olivine typically crystallizes in a cubic system and has a high degree of cleavage.
Answer: False
Olivine crystallizes in the orthorhombic system and exhibits poor cleavage, typically breaking with a conchoidal fracture.
The streak produced by olivine when ground into a powder is typically dark brown.
Answer: False
The streak of olivine is typically white or colorless, not dark brown.
Olivine is optically classified as uniaxial and exhibits a negative optical character.
Answer: False
Olivine is optically biaxial and exhibits a positive optical character.
Olivine's density decreases significantly as its iron content increases.
Answer: False
The density of olivine actually increases as the iron content increases, due to iron's higher atomic mass compared to magnesium.
The name 'olivine' is primarily associated with which characteristic of the mineral?
Answer: Its characteristic color
The mineral is named 'olivine' due to its typical olive-green hue.
Which of the following describes the typical crystal habit of olivine?
Answer: Massive or granular crystalline habits
While euhedral crystals can form, olivine is frequently observed in massive or granular aggregates, particularly within igneous rocks.
What is the Mohs hardness of olivine?
Answer: 6.5 - 7.0
Olivine ranks between 6.5 and 7.0 on the Mohs scale of mineral hardness, indicating it is relatively hard and resistant to scratching.
Olivine's fracture behavior is best described as:
Answer: Conchoidal fracture
Olivine typically exhibits conchoidal fracture, breaking into smooth, curved surfaces, and possesses poor cleavage.
Olivine is a principal constituent of the Earth's upper mantle and is highly stable when exposed to surface weathering.
Answer: False
While olivine is a principal constituent of the Earth's upper mantle, it is notably unstable under surface weathering conditions and readily alters when exposed to the atmosphere.
Olivine is commonly found in felsic igneous rocks and is rare in mafic and ultramafic rocks.
Answer: False
Olivine is predominantly found in mafic and ultramafic igneous rocks, which are derived from magnesium and iron-rich magmas, and is typically rare in felsic igneous rocks.
Dunite is an ultramafic rock characterized by containing over 90% olivine.
Answer: True
This definition accurately describes dunite as an ultramafic rock composed primarily of olivine, often exceeding 90% of its mineral content.
Mg-rich olivine can coexist stably with silica minerals like quartz, whereas fayalite cannot.
Answer: False
The stability relationship is reversed: Mg-rich olivine reacts with silica to form orthopyroxene, while fayalite, the iron-rich endmember, can coexist stably with silica minerals.
Olivine's physical properties significantly influence the rheology of the Earth's lower mantle, driving plate tectonics.
Answer: False
Olivine's influence on rheology is primarily significant in the Earth's *upper* mantle, where it is the most abundant mineral. This rheological behavior is a key driver of plate tectonics.
What is the primary role of olivine in Earth's geology according to the provided text?
Answer: It is a primary component of the Earth's upper mantle.
Olivine is a principal mineral constituent of the Earth's upper mantle, and its physical properties significantly influence the rheology of this region, which drives plate tectonics.
Olivine is commonly found as a primary mineral in which types of terrestrial rocks?
Answer: Mafic and ultramafic igneous rocks
Olivine is a characteristic mineral of mafic and ultramafic igneous rocks, which form from magmas relatively rich in magnesium and iron and poor in silica.
Which of the following rock types is characterized by containing more than 90% olivine?
Answer: Dunite
Dunite is defined as an ultramafic rock composed almost entirely of olivine, typically exceeding 90% by volume.
How does the stability of Mg-rich olivine differ from fayalite in the presence of silica minerals?
Answer: Mg-rich olivine reacts to form orthopyroxene, while fayalite can coexist stably with silica.
Mg-rich olivine is unstable in the presence of silica and reacts to form orthopyroxene. Fayalite, however, can coexist stably with silica minerals like quartz.
What aspect of olivine's properties is crucial for driving plate tectonics?
Answer: Its influence on the rheology (flow behavior) of the upper mantle
As the dominant mineral in the shallow upper mantle, olivine's rheological properties directly influence mantle convection and thus drive plate tectonic movements.
According to the Goldich dissolution series, olivine is considered one of the most stable common minerals on Earth's surface.
Answer: False
The Goldich dissolution series ranks olivine among the less stable common minerals, indicating it weathers relatively quickly when exposed to surface conditions.
Olivine typically weathers and alters into the mineral serpentine in the presence of water.
Answer: False
While serpentine is a common alteration product of ultramafic rocks, olivine itself typically alters to iddingsite in the presence of water and oxygen, which is a mixture of clay minerals and iron oxides.
Olivine is frequently found in sedimentary rocks because it is highly resistant to weathering.
Answer: False
Olivine is rarely found in sedimentary rocks precisely because it is *not* highly resistant to weathering; it tends to alter and break down before it can be incorporated into sedimentary layers.
According to the Goldich dissolution series, olivine's weathering resistance places it among:
Answer: The less stable common minerals.
The Goldich dissolution series ranks minerals based on their resistance to chemical weathering. Olivine is positioned among the less stable minerals, indicating it weathers relatively rapidly under surface conditions.
What is the common alteration product of olivine on the Earth's surface when exposed to water?
Answer: Iddingsite
When olivine weathers in the presence of water and oxygen, it commonly alters to iddingsite, a mixture of secondary minerals including clays and iron oxides.
Why is olivine rarely found in sedimentary rocks?
Answer: It rapidly weathers and is seldom preserved.
Olivine's susceptibility to chemical weathering means it is typically altered or destroyed before it can be transported and deposited as a component of sedimentary rocks.
Experiments suggest that absorbed water within olivine drastically increases its resistance to solid flow under high pressure.
Answer: False
Conversely, experimental data indicate that absorbed water within olivine significantly *reduces* its resistance to solid flow under high pressures, impacting mantle dynamics.
Under increasing pressure, olivine first transforms into ringwoodite, then into wadsleyite, before decomposing into perovskite and ferropericlase.
Answer: False
The correct sequence of transformations under increasing pressure is: olivine transforms into wadsleyite (around 410 km depth), then wadsleyite transforms into ringwoodite (around 520 km depth), and finally, ringwoodite decomposes into silicate perovskite and ferropericlase (around 660 km depth).
The endothermic phase transition of ringwoodite decomposition into silicate perovskite and ferropericlase reinforces mantle flow across the 660 km boundary.
Answer: False
This endothermic decomposition reaction at the 660 km discontinuity *hinders* mantle flow, acting as a barrier between the upper and lower mantle, unlike exothermic transitions which tend to reinforce flow.
How does the presence of absorbed water affect olivine's behavior under high pressure deep within the Earth?
Answer: It drastically reduces olivine's resistance to solid flow.
Experimental studies demonstrate that absorbed water significantly lowers olivine's viscosity, facilitating solid flow within the deep Earth, which has implications for mantle hydration.
Which mineral is the first high-pressure polymorph of olivine encountered with increasing depth in the Earth's mantle?
Answer: Wadsleyite
As pressure increases, olivine transforms first into wadsleyite, a denser polymorph with a sorosilicate structure, typically occurring below approximately 410 km depth.
At approximately 660 km depth, what transformation occurs involving olivine's high-pressure polymorphs?
Answer: Ringwoodite decomposes into silicate perovskite and ferropericlase.
The major phase transition at the 660 km discontinuity involves the decomposition of ringwoodite into silicate perovskite and ferropericlase, marking a significant boundary in mantle convection.
How does the decomposition of ringwoodite into silicate perovskite and ferropericlase impact mantle convection?
Answer: It hinders mantle flow across the 660 km boundary.
This decomposition reaction is endothermic, meaning it absorbs heat. This absorption of heat leads to a density decrease, which impedes the upward flow of hot mantle material across the 660 km boundary.
The translucent variety of olivine utilized as a gemstone is historically known as chrysolite, a name derived from Greek words meaning 'gold' and 'stone'.
Answer: False
The translucent gemstone variety of olivine is known as peridot. While 'chrysolite' was an older historical name, it is not the primary term used today, and the name 'peridot' is derived from the French word for olivine.
High-quality gem-quality olivine has been notably sourced from deposits on Zabargad Island in the Atlantic Ocean.
Answer: False
Gem-quality olivine has been sourced from Zabargad Island, but this island is located in the Red Sea, not the Atlantic Ocean.
The presence of olivine in meteorites suggests it is a common mineral throughout the solar system.
Answer: True
Indeed, the detection of olivine in meteorites, as well as on the Moon and Mars, strongly indicates its widespread formation and abundance across various celestial bodies within our solar system.
Pallasites are a type of meteorite that contains olivine mixed with silicate material.
Answer: False
Pallasites are a specific class of stony-iron meteorites characterized by olivine crystals embedded within a matrix of iron-nickel metal, not silicate material.
The spectral signature of olivine has been detected in dust disks around young stars and in comet tails, confirmed by Stardust mission samples.
Answer: True
This observation is significant, indicating the presence of olivine in protoplanetary disks and cometary materials, providing insights into early solar system composition.
What is the common name for the translucent gemstone variety of olivine?
Answer: Peridot
The translucent, gem-quality variety of olivine is known as peridot. While historically referred to as chrysolite, peridot is the modern and widely accepted term.
Where is a significant deposit of high-quality gem-quality olivine mentioned as a source?
Answer: Zabargad Island in the Red Sea
Zabargad Island, located in the Red Sea, is cited as a notable source for high-quality gem-quality olivine.
The detection of olivine's spectral signature in space is significant because it indicates:
Answer: Widespread formation and presence throughout the solar system.
Observing olivine's spectral signature in various extraterrestrial environments, from asteroid dust to cometary tails, points to its common origin and prevalence throughout the solar system.
Dispersing fine-grained olivine on beaches is a proposed method for sequestering atmospheric carbon dioxide due to its rapid weathering.
Answer: True
This method, known as enhanced weathering, leverages olivine's relatively rapid reaction with CO₂ to form stable carbonates, contributing to carbon sequestration efforts. Further research also explores its use in sustainable cement production.
What environmental remediation strategy involves using olivine's rapid weathering?
Answer: Sequestering atmospheric carbon dioxide (CO2)
The enhanced weathering of olivine is being explored as a method to capture atmospheric CO₂ by reacting it to form stable carbonate minerals.
In the aluminum foundry industry, olivine sand is utilized for:
Answer: Creating casting molds with specific properties.
Olivine sand serves as a valuable material for casting molds in aluminum foundries due to its thermal stability and reduced steam generation compared to silica sands.
Why is olivine considered suitable for use in Finnish sauna stoves?
Answer: It is resistant to weathering and can withstand heating cycles.
Olivine's durability and resistance to thermal cycling make it an appropriate material for sauna stoves, where it absorbs and radiates heat effectively over repeated use.