Enter a player name to begin or load your saved progress.
The chemical formula for stishovite is SiO₂, identical to that of quartz.
Answer: True
Explanation: This statement is accurate. Stishovite shares the same chemical composition, silicon dioxide (SiO₂), as quartz, but possesses a different crystal structure due to the conditions under which it forms.
Stishovite is a polymorph of aluminum oxide (Al₂O₃).
Answer: False
Explanation: This statement is false. Stishovite is a polymorph of silicon dioxide (SiO₂), not aluminum oxide.
What fundamental information does the chemical formula SiO₂ convey about stishovite?
Answer: It is a compound of silicon and oxygen, but with a different structure than quartz.
Explanation: The formula SiO₂ indicates that stishovite is a compound composed solely of silicon and oxygen. It signifies that stishovite is a polymorph of silicon dioxide, sharing its chemical composition with other forms like quartz but differing in crystal structure.
What does the term 'polymorph' mean in the context of stishovite?
Answer: A different crystal structure form of the same chemical compound (SiO₂).
Explanation: The term 'polymorph' signifies that stishovite is one of several different crystal structure forms that silicon dioxide (SiO₂) can take, each having the same chemical composition but distinct physical properties.
Which of the following is cited as another crystalline polymorph of silicon dioxide (SiO₂) alongside stishovite?
Answer: Coesite
Explanation: Coesite is mentioned in the source material as another distinct crystalline polymorph of silicon dioxide (SiO₂), alongside stishovite and other forms.
Stishovite is characterized as a cubic polymorph of silicon dioxide.
Answer: False
Explanation: This statement is factually incorrect. Stishovite crystallizes in the tetragonal system, not the cubic system. Its polymorph status refers to its distinct crystal structure compared to other forms of SiO₂.
Stishovite's structure features silicon atoms bonded to four oxygen atoms, similar to quartz.
Answer: False
Explanation: This statement is incorrect. A key distinction of stishovite is that its silicon atoms are octahedrally coordinated, bonded to six oxygen atoms, a configuration necessitated by the high pressures under which it forms. Quartz, conversely, exhibits tetrahedral coordination where silicon is bonded to four oxygen atoms.
Stishovite's crystal structure is similar to that of titanium dioxide's rutile form.
Answer: True
Explanation: This statement is accurate. The crystal structure of stishovite is analogous to that of rutile (TiO₂), particularly in the octahedral coordination of the central cation.
The unit cell dimensions of stishovite are approximately a = 4.177 Å and c = 2.665 Å.
Answer: True
Explanation: This statement is accurate. The reported unit cell dimensions for stishovite are approximately a = 4.1772(7) Å and c = 2.6651(4) Å.
Stishovite's high density and hardness are primarily due to the tetrahedral coordination of silicon atoms.
Answer: False
Explanation: This statement is incorrect. The exceptional density and hardness of stishovite are a direct result of the octahedral coordination of silicon atoms, which allows for a more compact atomic arrangement compared to the tetrahedral coordination found in less dense silica polymorphs like quartz.
What is the principal crystallographic feature that differentiates the structure of stishovite from that of quartz?
Answer: Stishovite features silicon atoms in octahedral coordination (six oxygen neighbors).
Explanation: The primary structural distinction lies in the coordination geometry of the silicon atoms. In stishovite, silicon is octahedrally coordinated (bonded to six oxygen atoms), whereas in quartz, it is tetrahedrally coordinated (bonded to four oxygen atoms).
How does the coordination number of silicon in stishovite contrast with its coordination number in quartz?
Answer: Silicon has a coordination number of 6 in stishovite and 4 in quartz.
Explanation: In stishovite, silicon atoms exhibit octahedral coordination, being bonded to six oxygen atoms. In contrast, silicon atoms in quartz are tetrahedrally coordinated, bonded to four oxygen atoms.
The crystal structure of stishovite bears a resemblance to that of which other mineral?
Answer: Rutile (TiO₂)
Explanation: Stishovite's crystal structure is analogous to that of rutile (TiO₂), a mineral form of titanium dioxide, particularly in the coordination geometry of the central cation.
What are the unit cell dimensions for stishovite as reported in the source material?
Answer: a = 4.1772(7) Å, c = 2.6651(4) Å
Explanation: According to the source, the unit cell dimensions for stishovite are approximately a = 4.1772(7) Å and c = 2.6651(4) Å.
Stishovite is known for its extreme softness, ranking low on the Mohs scale.
Answer: False
Explanation: This statement is incorrect. Stishovite is exceptionally hard, measuring 9.5 on the Mohs scale, which is significantly higher than most common minerals.
Pure stishovite exhibits a deep blue color.
Answer: False
Explanation: This statement is false. Pure stishovite is colorless. Coloration in natural samples is typically due to impurities or inclusions.
Stishovite exhibits a vitreous luster, meaning it has a dull, earthy appearance.
Answer: False
Explanation: This statement is incorrect. Vitreous luster describes a glassy, shiny appearance, not a dull or earthy one. Stishovite possesses a vitreous luster.
The specific gravity of stishovite is significantly lower than that of quartz.
Answer: False
Explanation: This statement is incorrect. Stishovite has a significantly higher specific gravity (approximately 4.29-4.35) than quartz (approximately 2.65) due to its denser crystal structure.
Stishovite has a lower specific gravity than seifertite.
Answer: False
Explanation: This statement is false. Stishovite (specific gravity ~4.29-4.35) is the second densest polymorph of silica, surpassed only by seifertite, implying stishovite has a higher specific gravity than most other silica polymorphs, but seifertite is denser.
Stishovite is optically uniaxial with a negative sign.
Answer: False
Explanation: This statement is incorrect. Stishovite is optically uniaxial, but it exhibits a positive (+) optical sign, not a negative one.
Stishovite's birefringence is approximately 0.027.
Answer: True
Explanation: This statement is true. The birefringence, the difference between the highest and lowest refractive indices, is a key optical property of stishovite and is reported as approximately 0.027.
Stishovite is transparent to opaque.
Answer: False
Explanation: This statement is false. Stishovite is typically described as transparent to translucent. While impurities can affect clarity, it is not generally considered opaque.
Stishovite is the densest known polymorph of silica.
Answer: False
Explanation: This statement is false. Stishovite is the second densest known polymorph of silica, surpassed only by seifertite.
What is the Mohs hardness value for stishovite?
Answer: 9.5
Explanation: Stishovite possesses a Mohs hardness of 9.5, making it exceptionally hard and one of the hardest known naturally occurring mineral substances.
Which of the following statements accurately describes a physical property of stishovite?
Answer: It is colorless when pure and has a vitreous luster.
Explanation: The statement that pure stishovite is colorless and exhibits a vitreous luster is true. Impurities can lead to coloration, but pure samples are colorless with a glassy shine.
What is the specific gravity value reported for synthetic stishovite?
Answer: 4.35
Explanation: The specific gravity of synthetic stishovite is reported as 4.35.
What is the measured birefringence of stishovite?
Answer: 0.027
Explanation: The birefringence of stishovite, representing the difference between its extraordinary and ordinary refractive indices, is approximately 0.027.
What is the significance of stishovite being the second densest known polymorph of silica?
Answer: It highlights its highly compact crystal structure due to octahedral silicon coordination.
Explanation: Its status as the second densest silica polymorph underscores stishovite's highly compact crystal structure, which is a direct consequence of the octahedral coordination of silicon atoms. This packing efficiency allows for greater density compared to less compressed forms of SiO₂.
What is the calculated specific gravity value for stishovite?
Answer: 4.29
Explanation: The calculated specific gravity for stishovite is reported as 4.29.
The high Vickers hardness of stishovite, approximately 30 GPa, indicates what about its structural properties?
Answer: Its structural properties are unique, especially under high pressure.
Explanation: This high hardness suggests that stishovite possesses unique structural properties, particularly under high-pressure conditions, which contribute to its resistance to deformation and scratching.
What is the typical diaphaneity, or transparency, of stishovite?
Answer: Transparent to translucent
Explanation: Stishovite is described as being transparent to translucent, indicating it allows light to pass through but may scatter it to some degree.
Stishovite is stable under normal atmospheric temperature and pressure conditions.
Answer: False
Explanation: This statement is false. Stishovite is metastable under normal conditions. It exists because the transformation kinetics to more stable polymorphs, such as quartz, are exceedingly slow at ambient temperatures and pressures.
Stishovite is resistant to chemical attack by hydrogen fluoride (HF).
Answer: True
Explanation: This statement is correct. Stishovite exhibits resistance to hydrogen fluoride (HF), a characteristic that distinguishes it from quartz, which readily reacts with this acid.
Stishovite forms under conditions of low pressure and high temperature.
Answer: False
Explanation: This statement is incorrect. Stishovite forms under conditions of extremely high pressure (exceeding 10 GPa) and high temperature, typically associated with meteorite impacts.
Stishovite decomposes when heated to its melting point.
Answer: True
Explanation: This statement is correct. Instead of melting congruently, stishovite decomposes when subjected to high temperatures approaching its melting point.
Under what specific geological conditions does stishovite typically form naturally?
Answer: Extremely high shock pressures, often associated with meteorite impacts.
Explanation: Naturally, stishovite forms under conditions of extremely high shock pressures, often exceeding 10 GPa, and elevated temperatures, typically associated with hypervelocity meteorite impacts into quartz-bearing rocks.
What is the reason stishovite is considered metastable under normal ambient conditions?
Answer: It slowly transforms into more stable polymorphs like quartz over time.
Explanation: Stishovite is metastable under normal conditions because, although it can exist, it has a tendency to slowly transform into more thermodynamically stable polymorphs of SiO₂, such as quartz, over geological timescales.
Which of the following is NOT considered a characteristic property of stishovite?
Answer: Stability under normal surface conditions
Explanation: Stability under normal surface conditions is not a characteristic of stishovite; it is metastable and tends to revert to more stable forms over time.
What is the chemical reactivity of stishovite when exposed to hydrogen fluoride (HF)?
Answer: It is resistant to HF, unlike quartz.
Explanation: Stishovite exhibits resistance to hydrogen fluoride (HF), a characteristic that distinguishes it from quartz, which readily reacts with this acid.
What thermal behavior does stishovite exhibit when heated near its melting point?
Answer: It decomposes.
Explanation: Instead of melting congruently, stishovite decomposes when subjected to high temperatures approaching its melting point.
Stishovite is a common mineral found abundantly on Earth's surface.
Answer: False
Explanation: This statement is false. Stishovite is a rare mineral on Earth's surface, typically found only under specific high-pressure conditions such as those created by meteorite impacts.
Large natural crystals of stishovite are relatively common.
Answer: False
Explanation: This statement is false. Large, intact crystals of stishovite are extremely rare; it is typically found as small fragments, usually measuring only 1 to 2 millimeters in length.
Stishovite can be found within diamonds, suggesting deep mantle formation.
Answer: True
Explanation: This statement is accurate. The presence of stishovite inclusions within diamonds is considered strong evidence that these diamonds originated under the extremely high pressures characteristic of the Earth's deep mantle.
Stishovite can be found as small fragments, typically up to 1-2 centimeters in length.
Answer: False
Explanation: This statement is false. While stishovite is found as fragments, the typical size is in the millimeter range (1-2 mm), not centimeters. This indicates the rarity of larger specimens.
The presence of stishovite inclusions within diamonds suggests that these diamonds originated from which geological environment?
Answer: They originated under exceptionally high-pressure conditions, likely deep within the Earth's mantle.
Explanation: The occurrence of stishovite within diamonds is considered strong evidence that these diamonds formed under the extremely high pressures characteristic of the Earth's deep mantle.
Under specific geological conditions, stishovite may be a predominant form of silicon dioxide in which region of the Earth?
Answer: The lower mantle
Explanation: Although rare on the surface, stishovite is hypothesized to be prevalent in the Earth's lower mantle due to the immense pressures present in that region.
The identification of 'post-stishovite phases' within ultra-high-pressure mantle rocks indicates what about the pressure conditions experienced by these rocks?
Answer: These rocks experienced pressures even higher than those required for stishovite formation.
Explanation: The presence of post-stishovite phases suggests that these mantle rocks experienced pressures even greater than those required for the formation of stishovite itself.
The description of stishovite being found as small fragments, typically 1 to 2 millimeters in length, implies what about its natural occurrence?
Answer: Large, intact crystals are extremely rare.
Explanation: This observation implies that large, intact crystals of stishovite are extremely rare in nature, with most specimens found as minute particles.
Stishovite was first synthesized in a laboratory by Sergey Stishov in 1961.
Answer: True
Explanation: This statement is accurate. Sergey Stishov, a Soviet high-pressure physicist, is credited with the first laboratory synthesis of stishovite in 1961.
Stishovite was first discovered in nature in the Ural Mountains in 1962.
Answer: False
Explanation: This statement is incorrect. While discovered in 1962, stishovite was first found in nature at Meteor Crater, Arizona, not the Ural Mountains.
Stishovite is named after the location where it was first discovered in nature, Meteor Crater.
Answer: False
Explanation: This statement is incorrect. Stishovite was named in honor of Sergey Stishov, the physicist who first synthesized it. Its natural discovery location was Meteor Crater, Arizona.
The IMA symbol assigned to stishovite is 'Sti'.
Answer: True
Explanation: This statement is accurate. 'Sti' is the official IMA (International Mineralogical Association) symbol designated for the mineral stishovite.
Who is credited with the initial laboratory synthesis of stishovite?
Answer: Sergey Stishov
Explanation: The first synthesis of stishovite in a laboratory setting is credited to Sergey Stishov in 1961.
In which specific geological location was stishovite first discovered in nature?
Answer: In Meteor Crater, Arizona.
Explanation: Stishovite was first discovered in nature within Meteor Crater, Arizona, in 1962.
What does the official IMA (International Mineralogical Association) symbol 'Sti' represent?
Answer: The official designation for the mineral stishovite.
Explanation: The IMA symbol 'Sti' serves as the official, standardized designation for the mineral stishovite, approved by the International Mineralogical Association Commission on New Minerals, Nomenclature and Classification.
What is the official IMA (International Mineralogical Association) symbol assigned to stishovite?
Answer: Sti
Explanation: The IMA symbol 'Sti' serves as the official, standardized designation for the mineral stishovite, approved by the International Mineralogical Association Commission on New Minerals, Nomenclature and Classification.
Stishovite belongs to the Oxides category within the Strunz classification system.
Answer: True
Explanation: This statement is accurate. The Strunz classification code 4.DA.40 places stishovite within the Oxides category, specifically the silica group.
Stishovite is classified under the Strunz system as 4.DA.40, placing it within the Silicates category.
Answer: False
Explanation: This statement is incorrect. The Strunz classification code 4.DA.40 designates stishovite as belonging to the Oxides category, specifically within the silica group, not the Silicates.
The Strunz classification code 4.DA.40 assigned to stishovite primarily indicates its membership in which mineral group?
Answer: Oxides
Explanation: The code 4.DA.40 in the Strunz classification system designates stishovite as belonging to the Oxides mineral group, specifically within the silica subgroup.
Within the Strunz classification system, the code 4.DA.40 for stishovite places it into which broad mineral category?
Answer: Oxides
Explanation: The Strunz classification code 4.DA.40 signifies that stishovite belongs to the Oxides mineral category.