What is a mineral, and how do we identify one from its physical properties?
Define a mineral and explain how physical properties (hardness, cleavage, luster, streak, color and density) and chemical composition are used to identify minerals, using the relevant Reference Tables charts.
A Regents answer on minerals: the definition of a mineral, the physical properties used to identify them (hardness, cleavage and fracture, luster, streak, color, density), why composition and internal arrangement control those properties, and how to use the Reference Tables Properties of Common Minerals chart, with worked exam questions.
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What this topic is asking
The Regents wants you to define a mineral and to identify minerals from their physical properties, using the Properties of Common Minerals chart in the Reference Tables. The core idea is that a mineral's orderly internal structure and fixed composition produce predictable, testable properties such as hardness, cleavage and density.
What a mineral is
The orderly atomic arrangement is the key idea: it is why a mineral grows into geometric crystals and why its physical properties are consistent and testable. The eight elements that make up most of Earth's crust by mass (in order) are oxygen, silicon, aluminum, iron, calcium, sodium, potassium and magnesium; oxygen and silicon together dominate, which is why the silicate minerals are the largest mineral group.
The physical properties used to identify minerals
Why composition and structure control 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) while weaker bonds in sheets make it soft and cleave easily (mica, graphite). The same element, carbon, forms both diamond (hardness 10) and graphite (hardness 1 to 2) 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.
Reading the Properties of Common Minerals chart
The Reference Tables chart lists, for each common mineral, its luster, hardness, cleavage or fracture, color, streak, distinguishing characteristics, use and chemical composition. To identify an unknown:
- Note the luster first (metallic or nonmetallic) to pick the right part of the chart.
- Test hardness against known references (fingernail, penny, glass).
- Check for cleavage (flat faces) or fracture.
- Use a distinguishing characteristic (calcite fizzes in acid; halite tastes salty and dissolves; magnetite is magnetic) to confirm.
Try this
Q1. State the five parts of the definition of a mineral. [2 points]
- 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 points]
- Cue. Small amounts of impurities change the color, so the same mineral can appear in several colors (quartz can be clear, pink, purple); structure-based properties such as cleavage and streak are more consistent.
Exam-style practice questions
Practice questions written in the style of NYSED exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
Regents (style)1 marksPart A. Which physical property is most useful for distinguishing the mineral galena from the mineral pyrite, since both are metallic and similar in color? (1) hardness (2) streak (3) luster (4) density. Justify your choice.Show worked answer →
A 1-point multiple-choice question. The answer is (2).
Both galena and pyrite have a metallic luster and a similar brassy-to-gray appearance, so luster (3) and color do not separate them well. Streak (2), the color of the powdered mineral on a streak plate, is reliably different: galena gives a gray-black streak and pyrite a greenish-black streak. Hardness (1) and density (4) also differ, but streak is the property the question targets as "most useful" because it is quick and the surface color of a metallic mineral can mislead. The trap is choosing color or luster, which look almost identical for these two.
Regents (style)2 marksPart B-2. A student tests a colorless mineral sample. It scratches glass but is scratched by a steel file, it breaks along flat surfaces in three directions not at right angles, and it fizzes in acid. Using the Properties of Common Minerals chart, identify the mineral and state two properties from the test that support your identification.Show worked answer →
A 2-point constructed-response question.
1 point: the mineral is calcite.
1 point: any two supporting properties, for example: it shows cleavage in three directions (rhombohedral cleavage), it reacts (fizzes) in acid, and its hardness is about 3 (scratched by a steel file but harder than a fingernail).
Markers reward naming calcite and citing properties that the chart lists for calcite (cleavage in three directions, effervescence in acid, hardness near 3). The acid fizz is the classic identifier for a carbonate. Do not just say "it is soft"; name the diagnostic test.
Related dot points
- Describe the rock cycle and explain how igneous rocks form from cooling magma or lava, using the Reference Tables Scheme for Igneous Rock Identification to relate texture, composition, color and density to the rock name.
A Regents answer on the rock cycle and igneous rocks: the three rock families and the processes that link them, how cooling rate controls crystal (grain) size, how the Scheme for Igneous Rock Identification relates texture, mineral composition, color and density to a rock name (granite, basalt, obsidian and others), with worked exam questions.
- Explain how sedimentary rocks form by compaction and cementation or by chemical and biologic processes, and how metamorphic rocks form by heat and pressure, using the Reference Tables charts to identify each by texture and composition.
A Regents answer on sedimentary and metamorphic rocks: clastic versus chemical and biologic sedimentary rocks, compaction and cementation, the role of fossils and sorting, foliated versus nonfoliated metamorphic rocks, contact and regional metamorphism, and how to use the Reference Tables identification charts, with worked exam questions.
- Describe the layered structure of Earth's interior and explain the theory of plate tectonics, including the evidence (sea-floor spreading, matching coastlines, fossils, magnetic stripes) and the calculation of plate spreading rate.
A Regents answer on Earth's interior and plate tectonics: the crust, mantle, outer and inner core and the Reference Tables inferred properties, mantle convection as the driver, the three boundary types, the evidence for sea-floor spreading (matching coastlines, fossils, magnetic stripes, age of sea floor), and a worked spreading-rate calculation.
- Explain Earth's rotation and revolution, the evidence for each, and how they produce the apparent daily motion of celestial objects at 15 degrees per hour, including the use of Polaris to find latitude.
A Regents answer on Earth's rotation and revolution: the evidence for each, the apparent daily motion of the Sun, Moon and stars at 15 degrees per hour, Foucault's pendulum and the Coriolis effect, and how the altitude of Polaris gives an observer's latitude in the Northern Hemisphere.
- Distinguish physical from chemical weathering, explain the factors that control the rate of weathering (climate, surface area, rock type), and describe how weathering and other processes form soil.
A Regents answer on weathering and soil: physical (mechanical) weathering such as frost wedging versus chemical weathering such as carbonation and oxidation, how climate, surface area and rock type control the rate, why warm wet climates weather chemically faster, and how soil forms as a mix of weathered rock and organic matter, with worked exam questions.
Sources & how we know this
- Reference Tables for Physical Setting/Earth Science (2011 edition) — New York State Education Department (2011)
- Regents Examination in Physical Setting/Earth Science — New York State Education Department (2026)