Mineral Property Reference
Seventeen common minerals — hardness, specific gravity, and crystal system, computed live from the same Mohs hardness, specific gravity, and crystal system logic those calculators use, plus what each combination is actually diagnostic of.
Hardness, specific gravity, and crystal system, by mineral
| Mineral | Mohs hardness | Comparable index minerals | Specific gravity | SG band | Crystal system |
|---|---|---|---|---|---|
| Halite | 2–2.5 | Gypsum, Calcite | 2.17 | low | Cubic (Isometric) |
| Pyrite | 6–6.5 | Orthoclase Feldspar, Quartz | 5.01 | dense | Cubic (Isometric) |
| Fluorite | 4 | Fluorite | 3.18 | moderate | Cubic (Isometric) |
| Galena | 2.5 | Gypsum, Calcite | 7.50 | very dense | Cubic (Isometric) |
| Sphalerite | 3.5–4 | Calcite, Fluorite | 4.00 | moderate | Cubic (Isometric) |
| Garnet (almandine group) | 7–7.5 | Quartz, Topaz | 4.20 | dense | Cubic (Isometric) |
| Magnetite | 5.5–6.5 | Apatite, Orthoclase Feldspar, Quartz | 5.18 | dense | Cubic (Isometric) |
| Sodalite | 5.5–6 | Apatite, Orthoclase Feldspar | 2.27 | low | Cubic (Isometric) |
| Quartz | 7 | Quartz | 2.65 | common | Hexagonal |
| Calcite | 3 | Calcite | 2.71 | common | Hexagonal |
| Topaz | 8 | Topaz | 3.53 | moderate | Orthorhombic |
| Beryl | 7.5–8 | Quartz, Topaz | 2.76 | common | Hexagonal |
| Zircon | 6.5–7.5 | Orthoclase Feldspar, Quartz, Topaz | 4.65 | dense | Tetragonal |
| Gypsum | 2 | Gypsum | 2.32 | low | Monoclinic |
| Malachite | 3.5–4 | Calcite, Fluorite | 3.80 | moderate | Monoclinic |
| Orthoclase Feldspar | 6 | Orthoclase Feldspar | 2.56 | common | Monoclinic |
| Albite (plagioclase feldspar) | 6–6.5 | Orthoclase Feldspar, Quartz | 2.62 | common | Triclinic |
“Comparable index minerals” is whichever of the Mohs scale’s ten reference minerals fall inside this mineral’s published hardness range, from the same mineralsInRange() function the hardness estimator uses. SG band is the same low / common / moderate / dense / very-dense classification the specific gravity calculator returns for that value.
What each mineral’s combination actually tells you
Halite
Cubic cleavage, a hardness a fingernail can mark, and a low SG separate halite from similar clear/white minerals like calcite or gypsum. Never confirm it by taste — the old "lick it, it's salty" field test cannot tell edible halite apart from a toxic look-alike, and it's worth retiring the habit entirely.
Pyrite
Cubic or pyritohedral crystal faces (often finely striated), a hardness that shrugs off a knife, and an SG around 5 separate "fool's gold" from real gold instantly — native gold is both much denser (SG ~19) and far softer (H2.5–3).
Handling note: Weathering pyrite can oxidize and give off a faint sulfurous smell and mild acidity ("pyrite disease"); store specimens dry rather than damp.
Fluorite
Perfect octahedral cleavage, an index-mineral hardness of 4, and a moderate SG are diagnostic on their own — and fluorite is the mineral fluorescence is named after, so it's worth a UV check too.
Galena
Cubic cleavage, a very high SG (~7.5) for such a soft mineral (H2.5), and a bright metallic luster are the classic galena signature.
Handling note: Galena is a lead sulfide. Wash your hands after handling it, avoid grinding or sanding it without dust control, and don't let a specimen sit somewhere a small child might mouth it.
Sphalerite
A resinous-to-adamantine luster, perfect cleavage in six directions, and a moderate-high SG with a hardness a knife scratches easily separate sphalerite from denser sulfides like galena or lighter silicates.
Garnet (almandine group)
A twelve- or twenty-four-sided crystal habit, a hardness that scratches quartz, and an elevated SG rule out most look-alike red or brown minerals at a glance.
Magnetite
Strong attraction to an ordinary magnet is a property almost nothing else on this list shares at that intensity, backed up by a metallic-to-submetallic luster and a high SG.
Sodalite
Deep blue color, often veined with white calcite, a hardness a steel file just barely handles, and a fairly low SG separate sodalite from denser blue minerals like azurite. The tenebrescent variety hackmanite is also a UV-lamp party trick worth trying.
Quartz
Quartz defines the H7 point on the Mohs scale itself, shows conchoidal fracture with no cleavage, and its SG of 2.65 is the benchmark most "common rock-forming mineral" comparisons are made against.
Quartz's true symmetry class is trigonal, but its commonly published unit cell uses the hexagonal setting shown here, which is why the identifier reports Hexagonal for it.
Calcite
Perfect rhombohedral cleavage in three directions, an index-mineral hardness of 3, and a brisk fizz in dilute acid (quartz shows none) make calcite one of the easiest common minerals to confirm with nothing more than a knife and vinegar.
Like quartz, calcite is truly trigonal but is usually published in this hexagonal-setting cell, so the identifier reports Hexagonal.
Topaz
An index-mineral hardness of 8 (scratches quartz easily) paired with one perfect basal cleavage and a moderate-high SG mark topaz. That single good cleavage direction is also a cutter's hazard: a sharp blow along it can split an otherwise tough-feeling crystal cleanly in two.
Beryl
A hexagonal prism habit, a hardness comfortably between quartz and topaz, and an SG around 2.8 identify the beryl family — the same species behind emerald and aquamarine, whose color comes from trace chromium/vanadium or iron rather than any difference in the underlying structure.
Handling note: Beryl contains beryllium. Cutting, grinding, or faceting it can produce a dust that's a genuine inhalation hazard; work wet, ventilate, and don't dry-grind it. A specimen just sitting on a shelf poses no such risk.
Zircon
An SG around 4.65 is unusually high for a mineral in this hardness range, which is part of why zircon gets mistaken for diamond at a glance — diamond is both harder (H10) and, despite that, less dense (SG 3.52), since SG tracks packing and atomic mass rather than hardness. Zircon commonly carries trace uranium and thorium, which is exactly what makes it useful for radiometric dating; an ordinary faceted or rough specimen poses no meaningful handling risk from that trace content.
Gypsum
The softest common index mineral (scratched by a fingernail), a very low SG, and — in its selenite variety — cleavage so perfect it splits into flexible, semi-transparent sheets, a combination nothing else on this list shares.
Malachite
Banded green color with a botryoidal or fibrous habit, moderate hardness, and an SG around 3.8 identify malachite.
Handling note: Malachite is a copper carbonate — not seriously toxic, but the dust from cutting, grinding, or polishing it (and its close relative azurite) shouldn't be inhaled. Work wet and ventilated, and wash your hands before eating.
Orthoclase Feldspar
The monoclinic member of the feldspar group and itself a Mohs index mineral, orthoclase's SG sits at the low end of the "common rock-forming" band alongside quartz and calcite — hardness and habit, not density, are what separate the feldspars from each other and from quartz in the field.
Albite (plagioclase feldspar)
A sodium plagioclase feldspar with no angle in its unit cell fixed at 90° — the textbook triclinic example. Albite is hard to separate from orthoclase by hardness or SG alone, since both cluster close together; fine parallel striations on a cleavage face (twinning) are usually the more reliable field tell.
Minerals that need more caution than this table shows
A handful of collectible minerals aren’t in the table above because getting their crystal-system geometry right would mean publishing precise crystallographic numbers with more confidence than is useful here — but they come up often enough in the hobby that they need a plain warning regardless of hardness or SG.
- Cinnabar(mercury sulfide) — never grind, cut dry, or heat it. Handle specimens with gloves, wash your hands afterward, and don’t store it near food or in a spot where dust could settle into living space.
- Realgar and orpiment (arsenic sulfides) — wash your hands after handling, avoid creating dust, and never taste-test. Realgar is also light-sensitive and slowly breaks down into a different, powdery arsenic mineral under normal light, which is one more reason not to handle a weathered surface carelessly.
- Autunite and uraninite(uranium-bearing, radioactive) — don’t store these in a living or sleeping area, keep them at a sensible distance if displayed, wash your hands after handling, and don’t rely on guesswork for anything you suspect is strongly radioactive — seek proper guidance rather than assuming.
- Asbestiform amphiboles and erionite— some amphibole minerals (and the zeolite erionite) grow in a fibrous, asbestos-like habit that is a serious inhalation hazard. Friable or fibrous specimens shouldn’t be cut, ground, or crumbled without proper respiratory protection; when a specimen looks fibrous and you’re not sure what it is, don’t work it at all.
Two habits apply across all of these, and across the whole hobby: never taste-test a mineral to identify it (the old “lick it to check for halite” trick can’t tell a safe mineral apart from a toxic look-alike), and wash your hands after any collecting or workbench session before you eat, drink, or touch your face.
Separately, cutting, grinding, tumbling, or dry-sawing any quartz-bearing rock — which is most rock — produces fine, invisible respirable crystalline silica. That’s the cause of silicosis, an irreversible lung disease, and it doesn’t announce itself the way a bad smell or visible dust cloud would. Wet-cut where you can, ventilate where you can’t, and use a properly fitted respirator rated for fine particulates — a paper dust mask doesn’t filter finely enough to help.
Frequently Asked Questions
Why do quartz and calcite show up as "Hexagonal" when every geology text calls them trigonal?
Both are genuinely trigonal minerals, but the unit cell most commonly published for them uses a hexagonal-shaped setting (two equal edges meeting at 120°) rather than the primitive rhombohedral cell (three equal edges, three equal angles that aren't 90°). The crystal system identifier classifies whichever cell geometry you feed it, and correctly reports Hexagonal for that setting — it isn't reclassifying the mineral's true symmetry class, it's describing the cell as given. See the seven crystal systems guide for the full explanation of why trigonal minerals are so often published this way.
Where do the hardness, SG, and crystal-system values in this table come from?
The hardness range, specific gravity, and unit-cell dimensions for each mineral are published mineralogical values. This page doesn't hand-classify them: it feeds the SG through the same classifySpecificGravity() function the SG calculator uses, feeds the cell through the same identifyCrystalSystem() function the crystal system identifier uses, and looks up comparable index minerals through the same mineralsInRange() function behind the Mohs estimator. A test in the codebase asserts every rendered value still matches a fresh call to those functions.
Why do some minerals have a hazard note and most don't?
Most common rock-forming minerals carry no meaningful health risk to collect or handle normally. A handful do — usually because they contain lead, arsenic, mercury, uranium, or beryllium, or because cutting/grinding them releases a dust that's a genuine inhalation hazard. Those get an explicit note. The absence of a note isn't a guarantee of zero risk for every possible variety or locality, just that the common form has no well-established specific hazard beyond ordinary field-safety practice.
Can I identify a mineral from this table alone?
Treat it as a cross-check, not a standalone ID. Two minerals can share a hardness range or a crystal system; combining hardness, SG, and crystal system narrows things a long way, but streak, luster, and cleavage still matter, especially when a specimen's numbers land between two candidates instead of matching one cleanly.
Published hardness, SG, and unit-cell figures vary slightly between sources, localities, and individual specimens. Treat every value here as a representative starting point for field comparison, not a certified assay of any one specimen you’re holding.
Use it with
- Mohs Hardness Estimator— run your own scratch tests and bracket a real specimen’s hardness the same way this table’s comparable-index-minerals column was generated.
- Specific Gravity Calculator — turn a weight-in-air and weight-in-water reading into the same SG figure and band shown here.
- Crystal System Identifier — classify your own measured unit cell into one of the seven systems.