Earth Science Quiz: Rock And Mineral Identification

What this quiz covers

This quiz focuses on Rock And Mineral Identification, giving you a quick way to practice the rules, question types, and explanations that matter most for Earth Science.

How to use this quiz

Try each quiz question before looking at the correct answer. Use the explanations to review missed ideas, then come back to similar questions until the pattern feels familiar.

Question 1

1. A talus slope at the base of a mountain, where rockfall debris accumulates. (correct answer)
2. A meandering river floodplain, where fine silt and clay settle out of suspension.
3. A deep-sea fan, where sediment is transported by turbidity currents over long distances.
4. A desert environment dominated by wind-blown sand dunes.

Explanation: The rock described is a breccia. The key features are the angularity of the clasts and the poor sorting. Angular clasts indicate very little transport from the source area, as transport by water or wind tends to round sharp edges. Poor sorting means a wide range of grain sizes are mixed together, which is also characteristic of minimal transport. A talus slope is an accumulation of rock debris directly at the base of a cliff, fitting these characteristics perfectly. River (B), deep-sea (C), and desert (D) environments all involve transport mechanisms that would result in better sorting and rounding of the clasts.

Question 2

1. High-grade regional metamorphism associated with deep burial and mountain building.
2. Contact metamorphism in the immediate vicinity of a large, hot magma intrusion.
3. Low- to intermediate-grade regional metamorphism involving directed pressure. (correct answer)
4. Low-pressure burial metamorphism in a rapidly subsiding sedimentary basin.

Explanation: The rock described is a phyllite. Its texture is intermediate between the dull slaty cleavage of slate and the coarse, visible mica flakes of schist. The silky sheen (phyllitic luster) and wavy foliation are characteristic. This texture develops under directed pressure during regional metamorphism. The grade is considered low-to-intermediate, higher than slate but lower than schist. The absence of index minerals like garnet and staurolite supports the conclusion that it has not reached high-grade conditions (A). Contact metamorphism (B) typically produces non-foliated rocks like hornfels because the pressure is not directed. Burial metamorphism (D) involves low-grade conditions but typically results in weaker foliation than seen in phyllite.

Question 3

1. ...the main component of rock salt deposits formed by evaporation.
2. ...a common alteration product from the chemical weathering of feldspars.
3. ...the dominant mineral composing most mature beach and desert sands. (correct answer)
4. ...easily dissolved by groundwater to form caves and other karst features.

Explanation: The described properties—high hardness (H=7, since it scratches steel H≈6.5 and glass H≈5.5), vitreous luster, and conchoidal fracture (breaking along curved surfaces) instead of cleavage—are all characteristic of quartz (SiO₂). The first part of the question requires identifying the mineral. The second part requires relating its properties to its geologic role. Because quartz is very hard and chemically resistant to weathering, it survives transport over long distances and becomes concentrated in sedimentary deposits after other less stable minerals (like feldspars and mafic minerals) have weathered away. This makes it the most common mineral in mature sands, such as those found on beaches and in desert dunes. Halite (A), clay minerals (B), and calcite (D) do not match the physical properties described.

Question 4

1. Magnetite, which concentrates in magmatic segregation deposits.
2. Hematite, which is a major constituent of banded iron formations. (correct answer)
3. Galena, which precipitates in low-temperature hydrothermal veins.
4. Sphalerite, which is often found in volcanogenic massive sulfide deposits.

Explanation: The combination of a reddish-brown streak and a specific gravity of ~5.0 are diagnostic for hematite (Fe₂O₃). While magnetite is also an iron ore, it is strongly magnetic and has a black streak. Galena has a much higher specific gravity (~7.5) and a gray streak. Sphalerite has a pale yellow to brown streak. Hematite is the principal iron mineral in banded iron formations (BIFs), which are chemically precipitated sedimentary rocks that are a major source of iron ore globally.

Question 5

1. A high-energy river channel where gravel and sand are deposited.
2. A restricted lagoon in an arid climate subject to high rates of evaporation. (correct answer)
3. A deep marine basin far from land and below the calcite compensation depth.
4. A glacial environment where unsorted till is deposited at the terminus of an ice sheet.

Explanation: The properties described (transparent, cleavage, softer than glass, no reaction to acid, dissolves in water) are characteristic of halite (NaCl). Halite is an evaporite mineral, meaning it precipitates from water as it evaporates. This process occurs in environments like restricted lagoons or playa lakes in arid climates where water inflow is less than evaporation. A river channel (A) would dissolve halite. A deep marine basin (C) is characterized by fine-grained pelagic sediments, not evaporites. A glacial environment (D) deposits physically weathered, unsorted debris (till).

Question 6

1. The original shale deposit was chemically different from west to east, leading to the formation of different metamorphic rocks.
2. The region was subjected to a uniform temperature and pressure, but for varying durations of time from west to east.
3. The intensity of metamorphism, including both temperature and pressure, progressively increased from west to east. (correct answer)
4. The western part of the region was buried more deeply than the eastern part during metamorphism.

Explanation: The sequence slate → schist → gneiss represents an increase in metamorphic grade. Slate is a low-grade metamorphic rock, schist is intermediate-grade, and gneiss is high-grade. The presence of garnet in the schist further confirms intermediate- to high-grade conditions. This systematic change indicates that the metamorphic conditions (temperature and pressure) were not uniform across the region but instead increased in intensity from west to east. This could be due to deeper burial or proximity to a magmatic heat source in the east. (A) is less likely than the classic grade progression. (B) is incorrect because grade is primarily a function of intensity, not duration. (D) is the opposite of what the evidence suggests.

Question 7

1. Gold, which is commonly found in placer deposits after weathering from its source rock.
2. Chalcopyrite, an ore of copper often found with other sulfides in hydrothermal veins.
3. Biotite mica, a common rock-forming mineral in granites and metamorphic rocks.
4. Pyrite, which frequently forms in sulfur-rich, reducing environments such as hydrothermal systems. (correct answer)

Explanation: The key properties are the greenish-black streak and high hardness. Gold (A) has a yellow streak and is very soft (H≈2.5-3). Chalcopyrite (B) has a similar color and streak but is much softer (H≈3.5-4) and would not scratch a steel file. Biotite mica (C) has a different habit (platy cleavage) and is soft (H≈2.5-3). Pyrite (FeS₂), also known as 'fool's gold', has a pale brass-yellow color, a greenish-black streak, and a hardness of 6-6.5, allowing it to scratch a steel file. Pyrite is a common sulfide mineral formed in a variety of environments, including hydrothermal veins and oxygen-poor sedimentary settings.

Question 8

1. A mid-ocean ridge where oceanic crust is being formed.
2. An oceanic hotspot track, such as the Hawaiian Islands.
3. A continental arc, where magma forms above a subducting oceanic plate. (correct answer)
4. A transform fault boundary connecting two oceanic ridge segments.

Explanation: The described rock is a granite. Its light color and mineralogy (quartz, K-feldspar) indicate a felsic composition, and its coarse-grained (phaneritic) texture indicates slow cooling deep underground (intrusive). Felsic magmas are typically generated by the partial melting of continental crust or by differentiation of magmas in settings with thick crust. A continental arc, formed at a convergent plate boundary where an oceanic plate subducts beneath a continental plate, is the classic setting for the generation of large granitic batholiths. Mid-ocean ridges (A) and hotspots (B) produce mafic magmas (basalt/gabbro). Transform boundaries (D) generally do not produce significant volumes of magma.

Question 9

1. A shallow, high-energy coral reef with abundant skeletal debris.
2. A deep, low-energy marine setting far from terrestrial sediment input. (correct answer)
3. A desert playa lake where chemical precipitates form during evaporation.
4. An alluvial fan where coarse sediments are deposited at the mouth of a canyon.

Explanation: Chalk is a biogenic sedimentary rock formed from the accumulation of coccoliths, the calcite plates of microscopic planktonic algae. These organisms live in the surface waters of the open ocean. When they die, their tiny shells rain down on the seafloor. For a pure chalk to form, this 'rain' of biogenic calcite must not be diluted by clastic sediment (sand, silt, clay) from land. This occurs in deep-marine environments far from continental margins. A coral reef (A) produces limestone from larger organisms in a high-energy setting. A playa lake (C) produces evaporites. An alluvial fan (D) is a terrestrial environment with coarse clastic sediment.

Question 10

1. Sample A formed from a gas-rich pyroclastic flow, while Sample B formed from a gas-poor lava flow.
2. Sample A is the extrusive equivalent of Sample B; both rock types are characteristic products of volcanism at mid-ocean ridges. (correct answer)
3. Both samples cooled from the same magma body, but Sample A cooled more slowly than Sample B.
4. Sample A is an intrusive rock that formed the core of a volcano, while Sample B is a metamorphic rock formed from basalt.

Explanation: Basalt (fine-grained mafic) and gabbro (coarse-grained mafic) are an extrusive-intrusive igneous rock pair. This means they have the same chemical/mineralogical composition but different textures due to different cooling rates. Basalt forms from the rapid cooling of mafic lava at the Earth's surface (extrusive). Gabbro forms from the slow cooling of the same type of magma deep underground (intrusive). Mid-ocean ridges are locations where mafic magma is generated, erupting as basaltic pillow lavas on the seafloor and cooling slowly in magma chambers below to form gabbro. Thus, basalt is the extrusive equivalent of gabbro. (A) is incorrect as basalt is a lava flow rock. (C) has the cooling rates reversed. (D) misidentifies both rock types.

Question 11

1. Rock salt, a chemical sedimentary rock formed by evaporation.
2. Schist, a medium-grade foliated metamorphic rock. (correct answer)
3. Obsidian, a glassy extrusive igneous rock.
4. Chalk, a soft, fine-grained biogenic sedimentary rock.

Explanation: The properties described—hardness between 2.5 and 3.5, and perfect cleavage in one direction producing flexible sheets—are characteristic of the mica mineral group (e.g., muscovite or biotite). The question requires two steps: first, identify the mineral group, and second, identify the rock type where it is a prominent, large component. During medium-grade regional metamorphism, microscopic mica crystals in a lower-grade rock (like slate or phyllite) recrystallize and grow into large, visible, aligned flakes. This texture, with parallel alignment of large mica crystals, defines schist. Rock salt (A), obsidian (C), and chalk (D) do not contain mica as a primary component.

Question 12

1. X is quartz, Y is feldspar; the lines are stress fractures from tectonic activity.
2. X is plagioclase feldspar, Y is potassium feldspar; the lines are exsolution lamellae.
3. X is calcite, Y is dolomite; the lines are evidence of chemical weathering.
4. X is potassium feldspar, Y is plagioclase feldspar; the lines are striations due to polysynthetic twinning. (correct answer)

Explanation: This question tests your ability to identify feldspars and their distinguishing characteristics. When examining igneous rocks, feldspars are among the most common minerals you'll encounter, and recognizing their key features is essential for proper identification. The correct answer is D. Mineral X, being pink with smooth cleavage surfaces, is potassium feldspar (orthoclase or microcline). The pink color comes from trace amounts of iron, and potassium feldspars typically show clean, smooth cleavage planes. Mineral Y, described as milky white with fine parallel grooves, is plagioclase feldspar. Those characteristic parallel lines are striations caused by polysynthetic twinning - a crystal structure feature where alternating layers of the crystal are oriented differently, creating the lined appearance on cleavage surfaces. Answer A is incorrect because quartz lacks cleavage entirely (it shows conchoidal fracture), and the described minerals are specifically stated to be feldspars. Answer B reverses the mineral identifications - plagioclase shows striations while potassium feldspar has smooth surfaces, not the other way around. Additionally, exsolution lamellae would appear as broader bands, not fine lines. Answer C is wrong because calcite and dolomite are carbonate minerals, not feldspars, and chemical weathering doesn't create the systematic parallel grooves described. Remember this key distinction: plagioclase feldspar shows striations (fine parallel lines) on cleavage surfaces due to twinning, while potassium feldspar has smooth cleavage surfaces. This difference is one of the most reliable ways to distinguish these two important rock-forming minerals in hand samples.

Question 13

1. Basalt lava flows that have developed columnar jointing upon cooling.
2. Limestone formations that have been subjected to dissolution by acidic groundwater.
3. Thick beds of shale that are being weathered and eroded layer by layer.
4. Granite batholiths that formed deep underground and were later uplifted and exposed by erosion. (correct answer)

Explanation: When you encounter questions about landscape features and rock identification, focus on connecting the physical characteristics to the rock type and its formation history. The key clues here are the coarse-grained crystalline texture, mineral composition, dome shapes, and exfoliation weathering pattern. The description points directly to granite and its characteristic weathering. Granite is a coarse-grained igneous rock composed of quartz, feldspar, and biotite—exactly the minerals listed. When granite batholiths (large underground igneous intrusions) are exposed at the surface through uplift and erosion, they form distinctive rounded domes. The exfoliation process occurs because granite formed under high pressure deep underground, and when exposed to surface conditions, the release of pressure causes the outer layers to expand and peel off in concentric sheets, creating the characteristic dome shapes. Choice A is incorrect because basalt is fine-grained (not coarse-grained) and forms columnar joints, not rounded domes with exfoliation. Choice B fails because limestone is sedimentary, not crystalline igneous rock, and dissolution creates caves and sinkholes, not domed landscapes. Choice C is wrong since shale is a fine-grained sedimentary rock that weathers in flat layers along bedding planes, not in the curved sheets of exfoliation. Remember that granite landscapes are easily identified by three key features: the coarse-grained texture with visible quartz and feldspar crystals, the rounded dome topography, and the onion-skin exfoliation weathering pattern. These features together indicate deep igneous intrusion followed by exposure through erosion.

Question 14

1. Dolostone, which often forms when magnesium-rich groundwater alters pre-existing limestone. (correct answer)
2. Limestone, which consists of calcite precipitated by marine organisms.
3. Rock Gypsum, which forms from the direct evaporation of sulfate-rich seawater.
4. Kaolinite (claystone), which forms from the chemical weathering of feldspar minerals.

Explanation: When you encounter mineral identification questions, focus on the physical and chemical properties as diagnostic clues. This question tests your ability to connect hardness, acid reactivity, and formation processes to identify carbonate rocks. The key observations here point to dolostone. The low hardness (scratched by fingernail) indicates a carbonate mineral, as both calcite and dolomite have hardness around 3-4, making them relatively soft. The critical clue is the acid test behavior: no reaction with solid rock but weak fizzing when powdered. This is characteristic of dolomite (CaMg(CO₃)₂), which reacts much more slowly with cold dilute HCl than calcite does. Powdering increases surface area, allowing the sluggish reaction to become visible. Dolostone commonly forms when magnesium-rich groundwater chemically alters existing limestone through a process called dolomitization. Looking at the wrong answers: (B) Limestone would fizz vigorously even as a solid piece since calcite reacts readily with cold HCl. (C) Rock gypsum has the right hardness but contains no carbonates, so it wouldn't fizz with acid at all. (D) Kaolinite claystone also lacks carbonates and wouldn't react with acid, plus it forms through feldspar weathering, not from groundwater alteration of carbonates. Remember this diagnostic sequence for carbonate rock identification: test hardness first (fingernail scratch suggests carbonates), then use acid reactivity to distinguish between limestone (vigorous fizzing) and dolostone (weak or delayed fizzing, especially when powdered).

Question 15

1. ...was a high-energy setting dominated by strong, unidirectional currents.
2. ...was continuously submerged in deep, quiet water.
3. ...was located at the base of a melting glacier.
4. ...was subjected to periodic wetting and subsequent aerial exposure and drying. (correct answer)

Explanation: The feature described is mud cracks. Mud cracks form when fine-grained, clay-rich sediment (mud) dries out and shrinks, causing it to crack. This process requires that the sediment be deposited in water and then later exposed to the air to dry. This cycle of wetting and drying is common in environments like tidal flats, river floodplains, and the edges of lakes in arid climates. High-energy currents (A) produce features like cross-bedding. Continuous submersion (B) would prevent the mud from drying. A glacial environment (C) deposits unsorted till.

Question 16

1. The original shale deposit was chemically different from west to east, leading to the formation of different metamorphic rocks.
2. The region was subjected to a uniform temperature and pressure, but for varying durations of time from west to east.
3. The intensity of metamorphism, including both temperature and pressure, progressively increased from west to east. (correct answer)
4. The western part of the region was buried more deeply than the eastern part during metamorphism.

Explanation: The sequence slate → schist → gneiss represents an increase in metamorphic grade. Slate is a low-grade metamorphic rock, schist is intermediate-grade, and gneiss is high-grade. The presence of garnet in the schist further confirms intermediate- to high-grade conditions. This systematic change indicates that the metamorphic conditions (temperature and pressure) were not uniform across the region but instead increased in intensity from west to east. This could be due to deeper burial or proximity to a magmatic heat source in the east. (A) is less likely than the classic grade progression. (B) is incorrect because grade is primarily a function of intensity, not duration. (D) is the opposite of what the evidence suggests.

Question 17

1. High-grade regional metamorphism associated with deep burial and mountain building.
2. Contact metamorphism in the immediate vicinity of a large, hot magma intrusion.
3. Low- to intermediate-grade regional metamorphism involving directed pressure. (correct answer)
4. Low-pressure burial metamorphism in a rapidly subsiding sedimentary basin.

Explanation: The rock described is a phyllite. Its texture is intermediate between the dull slaty cleavage of slate and the coarse, visible mica flakes of schist. The silky sheen (phyllitic luster) and wavy foliation are characteristic. This texture develops under directed pressure during regional metamorphism. The grade is considered low-to-intermediate, higher than slate but lower than schist. The absence of index minerals like garnet and staurolite supports the conclusion that it has not reached high-grade conditions (A). Contact metamorphism (B) typically produces non-foliated rocks like hornfels because the pressure is not directed. Burial metamorphism (D) involves low-grade conditions but typically results in weaker foliation than seen in phyllite.

Question 18

1. Sample A formed from a gas-rich pyroclastic flow, while Sample B formed from a gas-poor lava flow.
2. Sample A is the extrusive equivalent of Sample B; both rock types are characteristic products of volcanism at mid-ocean ridges. (correct answer)
3. Both samples cooled from the same magma body, but Sample A cooled more slowly than Sample B.
4. Sample A is an intrusive rock that formed the core of a volcano, while Sample B is a metamorphic rock formed from basalt.

Explanation: Basalt (fine-grained mafic) and gabbro (coarse-grained mafic) are an extrusive-intrusive igneous rock pair. This means they have the same chemical/mineralogical composition but different textures due to different cooling rates. Basalt forms from the rapid cooling of mafic lava at the Earth's surface (extrusive). Gabbro forms from the slow cooling of the same type of magma deep underground (intrusive). Mid-ocean ridges are locations where mafic magma is generated, erupting as basaltic pillow lavas on the seafloor and cooling slowly in magma chambers below to form gabbro. Thus, basalt is the extrusive equivalent of gabbro. (A) is incorrect as basalt is a lava flow rock. (C) has the cooling rates reversed. (D) misidentifies both rock types.

Question 19

1. Rock salt, a chemical sedimentary rock formed by evaporation.
2. Schist, a medium-grade foliated metamorphic rock. (correct answer)
3. Obsidian, a glassy extrusive igneous rock.
4. Chalk, a soft, fine-grained biogenic sedimentary rock.

Explanation: The properties described—hardness between 2.5 and 3.5, and perfect cleavage in one direction producing flexible sheets—are characteristic of the mica mineral group (e.g., muscovite or biotite). The question requires two steps: first, identify the mineral group, and second, identify the rock type where it is a prominent, large component. During medium-grade regional metamorphism, microscopic mica crystals in a lower-grade rock (like slate or phyllite) recrystallize and grow into large, visible, aligned flakes. This texture, with parallel alignment of large mica crystals, defines schist. Rock salt (A), obsidian (C), and chalk (D) do not contain mica as a primary component.

Question 20

1. X is quartz, Y is feldspar; the lines are stress fractures from tectonic activity.
2. X is plagioclase feldspar, Y is potassium feldspar; the lines are exsolution lamellae.
3. X is calcite, Y is dolomite; the lines are evidence of chemical weathering.
4. X is potassium feldspar, Y is plagioclase feldspar; the lines are striations due to polysynthetic twinning. (correct answer)

Explanation: This question tests your ability to identify feldspars and their distinguishing characteristics. When examining igneous rocks, feldspars are among the most common minerals you'll encounter, and recognizing their key features is essential for proper identification. The correct answer is D. Mineral X, being pink with smooth cleavage surfaces, is potassium feldspar (orthoclase or microcline). The pink color comes from trace amounts of iron, and potassium feldspars typically show clean, smooth cleavage planes. Mineral Y, described as milky white with fine parallel grooves, is plagioclase feldspar. Those characteristic parallel lines are striations caused by polysynthetic twinning - a crystal structure feature where alternating layers of the crystal are oriented differently, creating the lined appearance on cleavage surfaces. Answer A is incorrect because quartz lacks cleavage entirely (it shows conchoidal fracture), and the described minerals are specifically stated to be feldspars. Answer B reverses the mineral identifications - plagioclase shows striations while potassium feldspar has smooth surfaces, not the other way around. Additionally, exsolution lamellae would appear as broader bands, not fine lines. Answer C is wrong because calcite and dolomite are carbonate minerals, not feldspars, and chemical weathering doesn't create the systematic parallel grooves described. Remember this key distinction: plagioclase feldspar shows striations (fine parallel lines) on cleavage surfaces due to twinning, while potassium feldspar has smooth cleavage surfaces. This difference is one of the most reliable ways to distinguish these two important rock-forming minerals in hand samples.