What makes something a mineral, and how do you identify one from its properties?
Define a mineral and identify common rock-forming and ore minerals from their physical properties, including hardness, luster, streak, cleavage, color and density (Virginia 2018 Earth Science SOL ES.4).
A SOL-level answer on minerals for the Virginia Earth Science EOC: the five-part definition of a mineral, the physical properties used to identify them (hardness, luster, streak, cleavage and fracture, color, density), the major mineral groups led by the silicates, and why structure-based properties beat color, with worked exam questions.
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What this topic is asking
Virginia Earth Science SOL standard ES.4 asks you to define a mineral and to identify common rock-forming and ore minerals from their physical properties. The EOC tests this with drag-and-drop matching, hot-spot items on a properties chart, and multiple-choice questions that describe an unknown and ask what it is. The core idea is that a mineral's fixed composition and orderly internal structure give it predictable, testable properties, and that structure-based properties (hardness, cleavage, streak) are more reliable than color.
What a mineral is
The orderly atomic arrangement is the key idea: it is why a mineral can grow into geometric crystals and why its physical properties are consistent. By this definition, ice in a glacier is a mineral, but coal (organic) and glass (no orderly structure) are not. The eight most abundant elements in Earth's crust by mass are oxygen, silicon, aluminum, iron, calcium, sodium, potassium and magnesium; oxygen and silicon dominate, which is why silicate minerals are the largest group.
The physical properties used to identify minerals
Mineral groups
Minerals are grouped by chemical composition. The silicates (containing silicon and oxygen) are by far the largest group and include the common rock-forming minerals quartz, feldspar, mica, amphibole, pyroxene and olivine. Other groups are the carbonates (calcite, the main mineral in limestone, which fizzes in acid), oxides (hematite and magnetite, iron ores), sulfides (pyrite, galena), sulfates (gypsum), halides (halite, rock salt), and native elements (gold, copper, graphite, diamond). On the EOC, "the most common group of rock-forming minerals" is the silicates.
Why structure controls the properties
Two things set a mineral's properties: what atoms it contains (composition) and how those atoms are bonded and arranged (structure). Strong, evenly spaced bonds make a mineral hard (diamond, hardness 10); weak bonds between sheets make a mineral soft and able to cleave easily (mica; graphite, hardness 1 to 2). The same element, carbon, forms both diamond and graphite purely because the atoms are arranged differently. This is also why density is constant for a given mineral: it reflects how tightly a fixed set of atoms is packed.
Try this
Q1. State the five parts of the definition of a mineral. [2]
- Cue. Naturally occurring, inorganic, solid, definite chemical composition, orderly internal (crystalline) arrangement of atoms.
Q2. Explain why color is the least reliable property for identifying many minerals. [2]
- Cue. Small impurities change the color, so the same mineral can appear in several colors (quartz can be clear, pink or purple); structure-based properties such as streak, cleavage and hardness are more consistent.
Exam-style practice questions
Practice questions written in the style of VDOE exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
VA Earth Science SOL 2023 (style)1 marksWhich property is the most reliable for telling apart two minerals that both look metallic and brassy, such as pyrite and gold? (A) color. (B) luster. (C) streak. (D) shape.Show worked answer →
A 1-point multiple-choice item on mineral identification.
The correct answer is C. Pyrite and gold both have a metallic luster and a similar brassy color, so color (A) and luster (B) do not separate them. Streak (C), the color of the powdered mineral, is reliable: pyrite gives a greenish-black to black streak, while gold gives a yellow streak. Shape (D) can vary.
The test rewards using a structure-based property such as streak rather than the surface color, which can mislead (pyrite is "fool's gold").
VA Earth Science SOL 2024 (style)2 marksA clear mineral scratches glass but is scratched by a steel file, breaks with curved surfaces rather than flat faces, and is one of the most common minerals in Earth's crust. (a) Identify the mineral. (b) State two properties from the description that support your answer.Show worked answer →
A 2-point identification item.
(a) 1 point: the mineral is quartz.
(b) 1 point for any two supporting properties, for example: its hardness is about 7 (it scratches glass, hardness about 5.5, but is below the hardest minerals), it shows fracture (curved or conchoidal surfaces) rather than cleavage, and it is one of the most abundant minerals in the crust.
Markers reward naming quartz and citing two consistent properties (high hardness, fracture not cleavage, abundance). Do not rely on color, since quartz comes in many colors.
Related dot points
- Classify igneous, sedimentary and metamorphic rocks by how they form and explain the rock cycle, including how cooling rate, lithification, and heat and pressure transform rock (Virginia 2018 Earth Science SOL ES.5).
A SOL-level answer on rocks for the Virginia Earth Science EOC: how igneous, sedimentary and metamorphic rocks form, the link between cooling rate and crystal size, clastic versus chemical sediment, foliated versus nonfoliated metamorphic rock, and how the rock cycle transforms one type into another, with worked exam questions.
- Describe the compositional and physical layers of Earth's interior (crust, mantle, outer core, inner core; lithosphere and asthenosphere) and explain how seismic waves provide the evidence (Virginia 2018 Earth Science SOL ES.7).
A SOL-level answer on Earth's interior for the Virginia Earth Science EOC: the crust, mantle, outer core and inner core, the lithosphere and asthenosphere, the difference between continental and oceanic crust, and how P-waves and S-waves and the shadow zone reveal that the outer core is liquid, with worked exam questions.
- Distinguish renewable and non-renewable resources, describe the major energy sources and Virginia's mineral and energy resources, and evaluate the environmental impacts and conservation of resource use (Virginia 2018 Earth Science SOL ES.3 and ES.4).
A SOL-level answer on Earth's resources for the Virginia Earth Science EOC: renewable versus non-renewable, how fossil fuels form, nuclear and the alternatives (solar, wind, hydroelectric, geothermal), Virginia's coal, limestone, sand and gravel, and the environmental trade-offs and conservation of resource use, with worked exam questions.
- Distinguish mechanical and chemical weathering, identify the agents of erosion and deposition, and explain how particle size, sorting and water velocity control where sediment is deposited (Virginia 2018 Earth Science SOL ES.6 surface processes).
A SOL-level answer on surface processes for the Virginia Earth Science EOC: mechanical versus chemical weathering and what speeds each, the agents of erosion (water, wind, ice, gravity), how water velocity controls the size of sediment carried and deposited, sediment sorting and rounding, and landforms like deltas and moraines, with worked exam questions.
- Use appropriate tools and SI units to make and record measurements in Earth science, including length, mass, volume, temperature, time, air pressure, wind speed and rainfall (Virginia 2018 Earth Science SOL ES.1).
A SOL-level answer on measurement for the Virginia Earth Science EOC: the SI units for length, mass, volume, temperature and time, the instruments used in Earth science (thermometer, barometer, anemometer, rain gauge, graduated cylinder, balance), how to calculate density, and how to read instruments correctly, with worked exam questions.
Sources & how we know this
- 2018 Science Standards of Learning (Earth Science) — Virginia Department of Education (2018)
- SOL Practice Items (All Subjects) — Virginia Department of Education (2024)