Rocks and Minerals Practice Questions
20 free Rocks and Minerals practice questions for the General Science. Tap an option to answer — you get instant feedback, the correct answer, and a detailed explanation for every question.
Which of the following is the primary characteristic that defines a mineral?
- A It must be organic in origin.
- B It must have a fixed composition and a crystalline structure.
- C It must be liquid at room temperature.
- D It must be composed of at least three different chemical elements.
Correct answer: It must have a fixed composition and a crystalline structure.
By definition, a mineral is a naturally occurring, inorganic solid with a definite chemical composition and an ordered internal structure. Substances like glass lack this crystalline structure and are therefore not minerals.
What type of rock forms from the cooling and solidification of magma or lava?
- A Sedimentary
- B Metamorphic
- C Igneous
- D Clastic
Correct answer: Igneous
Igneous rocks are formed through the crystallization of molten rock. If they cool underground, they are intrusive (plutonic); if they cool on the surface, they are extrusive (volcanic).
On the Mohs scale of mineral hardness, which mineral serves as the standard for a hardness of 10?
- A Quartz
- B Topaz
- C Corundum
- D Diamond
Correct answer: Diamond
Diamond is the hardest naturally occurring mineral and is placed at 10 on the Mohs scale. Corundum follows it at 9, while quartz is significantly softer at 7.
Which process is responsible for the formation of sedimentary rocks like sandstone and shale?
- A High heat and pressure without melting
- B Compaction and cementation of fragments
- C Rapid cooling of silica-rich lava
- D Crystallization from a hydrothermal vent
Correct answer: Compaction and cementation of fragments
Sedimentary rocks form through lithification, where sediments undergo compaction from the weight of overlying layers and cementation as minerals precipitate in pore spaces. This typically happens in layers called strata.
A metamorphic rock that exhibits a layered or banded appearance is described as being:
- A Crystalline
- B Vesicular
- C Foliated
- D Glassy
Correct answer: Foliated
Foliation occurs when pressure causes platy or elongated minerals to align in parallel layers. Common examples of foliated metamorphic rocks include slate, schist, and gneiss.
Which mineral property is described by the tendency of a mineral to break along smooth, flat surfaces?
- A Fracture
- B Cleavage
- C Luster
- D Streak
Correct answer: Cleavage
Cleavage is the result of internal zones of weakness in the mineral's crystal lattice. If a mineral breaks irregularly rather than along flat planes, it is said to exhibit fracture.
The transformation of limestone into marble is an example of which geological process?
- A Rock weathering
- B Erosion
- C Metamorphism
- D Rock deposition
Correct answer: Metamorphism
Marble forms when limestone is subjected to high heat and pressure, causing the calcite crystals to recrystallize into a denser, interlocking texture. This is a classic example of non-foliated metamorphism.
Which type of igneous rock has a 'glassy' texture, indicating it cooled so quickly that no crystals had time to grow?
- A Granite
- B Basalt
- C Obsidian
- D Pumice
Correct answer: Obsidian
Obsidian forms from the extremely rapid cooling of lava. Because the atoms are frozen in place before they can arrange themselves into a crystalline lattice, the result is a volcanic glass.
What is the most abundant group of minerals found in the Earth's crust?
- A Carbonates
- B Sulfates
- C Silicates
- D Oxides
Correct answer: Silicates
Silicates, which are built around the silicon-oxygen tetrahedron (SiO4), make up approximately 90% of the Earth's crust. Common examples include quartz, feldspar, and mica.
Which of the following describes a 'clastic' sedimentary rock?
- A A rock formed from the remains of living organisms
- B A rock formed from minerals precipitating out of solution
- C A rock formed from broken fragments of earlier rocks
- D A rock formed directly from volcanic ash in water
Correct answer: A rock formed from broken fragments of earlier rocks
Clastic rocks are categorized by the size of the sediment particles they contain. Conglomerate, sandstone, and siltstone are all clastic rocks formed from the accumulation of solid debris.
Intrusive igneous rocks generally have larger crystals than extrusive igneous rocks because:
- A They contain more water.
- B They cool more slowly deep within the Earth.
- C They are subjected to higher pressure.
- D They are composed of different chemical elements.
Correct answer: They cool more slowly deep within the Earth.
Slower cooling allows more time for ions to migrate to crystal seeds, resulting in larger, visible crystals (phaneritic texture). Extrusive rocks cool quickly, resulting in small crystals (aphanitic texture) or no crystals at all.
Which of these minerals would be most likely to fizz (effervesce) when a drop of dilute hydrochloric acid is placed on it?
- A Quartz
- B Calcite
- C Halite
- D Gypsum
Correct answer: Calcite
Calcite is a carbonate mineral (CaCO3). It reacts with acid to release carbon dioxide gas, which causes the characteristic fizzing used as a field test for identifying limestone and marble.
The 'streak' of a mineral refers to:
- A The color of the mineral in its solid form
- B The color of the mineral in powdered form
- C The way the mineral reflects light
- D The pattern of light passing through the mineral
Correct answer: The color of the mineral in powdered form
A mineral's streak is often more reliable for identification than its outward color, which can be affected by impurities. It is tested by rubbing the mineral across an unglazed porcelain plate.
Which metamorphic rock is formed from the high-grade metamorphism of shale or granite and displays distinct color banding?
- A Slate
- B Phyllite
- C Schist
- D Gneiss
Correct answer: Gneiss
Gneiss represents a high grade of metamorphism where minerals segregate into light and dark bands (gneissose banding). This requires intense heat and pressure typically found in regional metamorphic zones.
What is the specific name for a sedimentary rock that is composed primarily of calcium carbonate from the shells of marine organisms?
- A Chert
- B Evaporite
- C Biochemical limestone
- D Breccia
Correct answer: Biochemical limestone
Limestone often forms biologically as organisms like coral and mollusks extract calcium carbonate from seawater. When these organisms die, their remains accumulate and eventually lithify into rock.
A rock that contains large crystals (phenocrysts) embedded in a matrix of much finer crystals is said to have a ______ texture.
- A Porphyritic
- B Pyroclastic
- C Vesicular
- D Pegmatitic
Correct answer: Porphyritic
Porphyritic texture indicates a complex cooling history: slow cooling initially (forming large crystals) followed by a rapid cooling phase (forming the fine-grained background).
Which of the following minerals is commonly known as 'fools gold' due to its metallic luster and brass-yellow color?
- A Lead galena
- B Iron pyrite
- C Black magnetite
- D Red hematite
Correct answer: Iron pyrite
Pyrite is an iron sulfide that often crystallizes into perfect cubes. While it looks like gold, it is much harder and has a different streak (greenish-black) compared to real gold (yellow).
What is the primary difference between a 'breccia' and a 'conglomerate'?
- A Breccia is igneous, while conglomerate is sedimentary.
- B Breccia's clasts are angular; conglomerate's are rounded.
- C Conglomerate forms from lava, while breccia forms from magma.
- D Breccia contains only one type of mineral.
Correct answer: Breccia's clasts are angular; conglomerate's are rounded.
Both are clastic sedimentary rocks with large particles. The roundness of grains in a conglomerate suggests they were transported a long distance by water, while the angular grains in a breccia suggest a short transport distance.
Which mineral is the primary source of common table salt?
- A Fluorite
- B Halite
- C Sylvite
- D Graphite
Correct answer: Halite
Halite is the mineral form of sodium chloride (NaCl). It is an evaporite mineral, meaning it typically forms from the evaporation of saline lake or sea water.
What happens to the density of a rock as it undergoes regional metamorphism?
- A It decreases as minerals expand.
- B It stays the same because no new matter is added.
- C It generally increases as atoms are packed more tightly.
- D It depends entirely on the color of the original parent rock.
Correct answer: It generally increases as atoms are packed more tightly.
High pressure causes the atoms in minerals to rearrange into more compact structures. Consequently, metamorphic rocks are usually denser and less porous than their parent rocks (protoliths).