3.1 Minerals

Why Minerals Matter on the Regents

Minerals are the chemical building blocks of every rock on Earth, so the Earth and Space Sciences Regents treats mineral identification as a foundation skill inside the Earth's Systems strand. Question clusters routinely give you a list of observed properties and ask you to name the mineral using the Properties of Common Minerals chart in the reference tables. Mastering this saves you from memorizing dozens of minerals: you reason from evidence instead.

What Counts as a Mineral

A mineral must satisfy five conditions. All five must be true, which is why ice can be a mineral while glass and coal cannot.

• Naturally occurring — formed by natural processes, not manufactured.
• Inorganic — not produced by living things (so coal, a fossil fuel, is excluded).
• Solid — not a liquid or gas at surface conditions.
• Definite chemical composition — expressible by a formula, such as quartz (SiO₂).
• Crystalline structure — atoms arranged in an orderly, repeating three-dimensional pattern. Volcanic glass fails here: it cooled too fast for atoms to organize, so it is not a mineral.

Physical Properties Used for Identification

Hardness and the Mohs Scale

Hardness is a mineral's resistance to being scratched. The Mohs hardness scale ranks ten reference minerals from 1 (softest) to 10 (hardest):

The scale is ordinal, not linear: diamond is far more than ten times harder than talc. A practical Regents move is to bracket a mineral. If a sample is scratched by a steel nail (5.5) but not by a fingernail (2.5), its hardness lies roughly between 2.5 and 5.5.

Cleavage versus Fracture

This pair is a classic Regents trap, so keep the distinction sharp. Cleavage is the tendency to break along smooth, flat, repeating planes determined by weak directions in the atomic structure; mica splitting into thin flexible sheets and halite breaking into cubes are cleavage. Fracture is irregular breakage with no flat planes, such as the curved, glassy (conchoidal) surfaces of quartz. The key idea: if breakage repeats in flat, parallel planes, it is cleavage; if it is rough or curved, it is fracture.

Luster, Streak, and Color

Luster describes how a mineral's surface reflects light and splits into two broad classes: metallic (shiny like polished metal, as in galena and pyrite) and nonmetallic (glassy, pearly, dull, or earthy). The Properties of Common Minerals chart sorts entries by luster first, so deciding metallic vs nonmetallic immediately cuts your options.

Streak is the color of a mineral's powder, seen by rubbing the sample across an unglazed porcelain streak plate. Streak is far more reliable than surface color because the powder color is consistent even when the visible sample varies. Pyrite, for example, looks gold but leaves a greenish-black to black streak, which is how you avoid the “fool's gold” mistake.

Color is the least reliable property because impurities change it. Quartz can be clear, pink (rose), purple (amethyst), or smoky while remaining the same mineral, so never identify on color alone.

Silicate Structure

Most of Earth's crust is built from silicate minerals. Their fundamental unit is the silicon–oxygen tetrahedron: one silicon atom bonded to four oxygen atoms in a pyramid (SiO₄). These tetrahedra link in chains, sheets, or full three-dimensional frameworks, and how they connect controls properties such as cleavage. Quartz is a framework silicate (hard, no cleavage, fractures); mica is a sheet silicate (cleaves into thin layers); feldspars are the most abundant crustal minerals. Knowing that silicates dominate the crust links directly to the rock chemistry you study in 3.2.

Using the ESRT Properties of Common Minerals Chart

Treat the chart as a decision tool. Read left to right: first note luster, then hardness, then cleavage or fracture, then color, distinguishing properties, use or name, and composition. Match the observed properties down the rows until only one mineral fits. A sample with metallic luster, a greenish-black streak, hardness near 6, and cubic cleavage points to pyrite on the chart, while a nonmetallic glassy mineral with hardness 7 and fracture points to quartz.

A Worked Identification

Suppose a cluster gives you these observations: nonmetallic luster, white to colorless streak, hardness about 3, breaks into rhombs (three cleavage directions, not at right angles), and fizzes in acid. Start at the luster column and discard all metallic entries. Move to hardness near 3, which is soft enough to be scratched by a copper penny. The diagnostic clue is the reaction with acid and the rhombic cleavage, which on the chart identify calcite (CaCO₃). Notice how no single property was enough — color was useless, but hardness plus cleavage plus the acid test converged on one answer. This is the reasoning the Regents rewards.

Common Regents Traps

Watch for these recurring pitfalls. First, glass and obsidian are not minerals because they lack an orderly crystalline structure, even though they look mineral-like. Second, color is a distractor: amethyst, rose quartz, and smoky quartz are all quartz, so a question that leans on color is usually testing whether you fall for it. Third, "fool's gold" (pyrite) is distinguished from real gold by its greenish-black streak and greater hardness, while gold leaves a gold streak and is very soft. Fourth, do not confuse cleavage with crystal shape: cleavage is about how a mineral breaks, not the shape it grew into.

Anchoring every identification to chart-based evidence keeps you out of these traps.