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Mineral Classification: How the Mineral Classes Work, from Native Elements to Silicates

By Digital Towns Crystals ยท Last reviewed October 8, 2026

Short answer: mineralogists sort minerals by chemistry, specifically by the dominant negatively charged part of the formula. That gives a short list of classes: native elements (copper, diamond), sulfides (pyrite), halides (fluorite, halite), oxides (hematite), carbonates (calcite, malachite), sulfates (barite, celestite, gypsum), phosphates and vanadates (apatite, vanadinite) and the silicates, which are split again by how their silicon and oxygen tetrahedra link. The two standard schemes are Dana and Nickel-Strunz.

Why sort minerals by chemistry rather than by color or shape?

Color is the least reliable property a mineral has, and crystal shape changes with growth conditions. Chemistry does not. Minerals that share an anion group tend to share behavior: carbonates react with acid, sulfides are usually metallic and dense, silicates are usually hard and glassy. So a class label tells a collector what to expect from a specimen before it is tested, and it tells a seller which neighbors in a drawer are likely to be confused with it.

Within a class, minerals are grouped again by structure. Calcite, rhodochrosite and smithsonite sit in the same calcite group because they share one crystal architecture with different metals swapped into it. That idea of a shared framework with substitutions runs through the whole system, and it is why the shape side of the story, covered in the guide to crystal systems, complements the chemistry here rather than replacing it.

What are Dana and Strunz, and why do the numbers differ?

Two catalogues dominate. The Dana system in its current form follows Dana's New Mineralogy, published by John Wiley and Sons in 1997, and Webmineral's Dana listing shows how far it subdivides: class 01 is native elements, class 02 sulfides, and the silicates do not begin until class 51. The Nickel-Strunz system (version 10 on Webmineral's Strunz page) uses just ten top-level numbers, from 01 Elements to 09 Silicates, with 10 reserved for organic compounds.

The two do not always agree, and quartz is the famous case. Webmineral's quartz record gives a Dana number of 75.01.03.01, a tectosilicate framework, and a Strunz number of 04.DA.05, which puts SiO2 among the oxides (Webmineral). Both readings are defensible: by formula quartz is silicon oxide, by structure it is a three-dimensional framework of linked tetrahedra, the same architecture as feldspar. When a label or database seems to contradict another, check which scheme it uses before assuming an error.

How to read a class number

A Strunz code such as 05.AB.05 reads from broad to narrow: 05 is the carbonate class, A means carbonates without additional anions and without water, B narrows the cation type, and the final digits pick out the group. Calcite carries exactly that code. Dana numbers work the same way in four parts; calcite is 14.01.01.01, read as anhydrous carbonates, simple formula, calcite group, first member (Webmineral).

Which minerals belong to each class?

The table below uses formulas and class codes from the individual Webmineral records, with familiar shop material as the examples.

Class (Strunz) Defining chemistry Shop examples Formula Strunz code
01 Elements one element, uncombined native copper, diamond Cu, C 01.AA.05, 01.CB.10a
02 Sulfides metal plus sulfur pyrite, galena FeS2, PbS 02.EB.05a, 02.CD.10
03 Halides metal plus a halogen (fluorine, chlorine) fluorite, halite CaF2, NaCl 03.AB.25, 03.AA.20
04 Oxides metal plus oxygen hematite, corundum, quartz Fe2O3, Al2O3, SiO2 04.CB.05, 04.CB.05, 04.DA.05
05 Carbonates CO3 group calcite, malachite, azurite CaCO3, Cu2(CO3)(OH)2 05.AB.05, 05.BA.10
07 Sulfates SO4 group (plus molybdates) barite, celestite, wulfenite BaSO4, SrSO4, PbMoO4 07.AD.35, 07.AD.35, 07.GA.05
08 Phosphates PO4, AsO4, VO4 groups apatite, vanadinite Ca5(PO4)3(OH,F,Cl), Pb5(VO4)3Cl 08.BN.05
09 Silicates SiO4 tetrahedra kyanite, beryl, feldspar, mica Al2SiO5, Be3Al2Si6O18 09.AF.15, 09.CJ.05

Native elements

Single elements standing alone. Webmineral's copper record gives the formula as plain Cu and the Dana number 01.01.01.03, in the gold group alongside silver and lead. Carbon appears twice: diamond and graphite share Dana group 01.03.06, identical chemistry with completely different structures, which is the clearest demonstration that a formula alone does not define a mineral.

Sulfides

Metals bonded to sulfur, usually opaque with a metallic luster. Webmineral lists pyrite as FeS2 with a Dana number of 02.12.01.01. Galena, the lead ore, is PbS. Most sulfides are dense, and many tarnish or break down in damp air, which ties this class to the pyrite care questions collectors ask most.

Halides

Here the anion is a halogen. Fluorite is CaF2, Strunz 03.AB.25, and halite is NaCl, Strunz 03.AA.20, under "Simple Halides, Without H2O" (Webmineral). Halite is a water-soluble salt; fluorite is not. The class name groups them by chemistry, not by how they behave in a sink.

Oxides and hydroxides

Metal plus oxygen. Hematite is Fe2O3 and shares the corundum-hematite group with corundum, Al2O3, the mineral behind ruby and sapphire (Webmineral). That shared group explains why the two have the same trigonal structure while looking nothing alike in a tray.

Carbonates

Built on the CO3 group. Calcite is the anchor. Malachite, Cu2(CO3)(OH)2, sits in Strunz 05.BA as a carbonate with additional anions, because it carries hydroxyl as well (Webmineral). Rhodochrosite, MnCO3, is a straight member of the calcite group. Copper carbonates like malachite and azurite are typical of the weathered upper parts of ore bodies, covered in the guide to oxidation zone minerals.

Sulfates, chromates and molybdates

Built on SO4 and its relatives. Webmineral's barite record places barite (BaSO4), celestine (SrSO4) and anglesite (PbSO4) together in Dana group 28.03.01, one structure with barium, strontium or lead in the metal site (Webmineral). Shops sell celestine as celestite. Gypsum, the mineral behind selenite, is a hydrated sulfate, Strunz 07.CD.40. Wulfenite surprises people: PbMoO4 is a molybdate, yet Strunz files it at 07.GA.05 inside the sulfate class (Webmineral).

Phosphates, arsenates and vanadates

Built on PO4 and chemically similar groups. Apatite and vanadinite share the code 08.BN.05: apatite is calcium phosphate with OH, F or Cl, and vanadinite, Pb5(VO4)3Cl, is the same hexagonal architecture with lead and vanadium (Webmineral).

How are the silicates divided?

Silicates get their own subdivision because there are so many of them. A BC open geology textbook, Physical Geology, states that the vast majority of the minerals that make up Earth's crust are silicates, all built from the silica tetrahedron: four oxygen atoms around one silicon, with a net charge of minus 4. What changes between subclasses is how many oxygens each tetrahedron shares with its neighbors.

Subclass How tetrahedra link Examples
Nesosilicates isolated, none shared olivine (peridot), garnet, zircon, kyanite
Sorosilicates pairs epidote, zoisite
Cyclosilicates rings tourmaline, beryl
Inosilicates single or double chains pyroxenes, rhodonite, amphiboles
Phyllosilicates sheets micas, clay minerals, chlorite
Tectosilicates 3D framework feldspars, quartz, zeolites

The linkage shows up in the hand. Sheet silicates such as muscovite (Strunz 09.EC.15, Webmineral) peel because bonding between the sheets is weak, which the textbook credits for their perfect one-direction cleavage. In quartz every oxygen is shared, giving a silicon to oxygen ratio of 1:2 and the hardness and lack of cleavage collectors rely on. Kyanite (Al2SiO5, Strunz 09.AF.15, Webmineral) is a nesosilicate, beryl (Be3Al2Si6O18, Strunz 09.CJ.05, Webmineral) is a six-membered ring silicate, and orthoclase feldspar (KAlSi3O8) carries Dana 76.01.01.01 as an aluminum and silicon framework (Webmineral).

Materials without an orderly structure, such as opal and obsidian, fall outside this scheme altogether; see mineraloids.

What does the class tell you about a specimen in practice?

Class predicts a handful of practical behaviors:

  • Acid reaction marks the carbonates. Geology.com's calcite page lists its powder as effervescing weakly in dilute HCl. Acid will etch a polished carbonate, so this is a test for rough material only.
  • A fizz can mislead. Geology.com's barite page describes students who saw massive barite fizz and called it calcite, when the reaction came from contamination left by a calcite hardness tool.
  • Heft points to heavy metals. Barite's name comes from the Greek "barys", meaning heavy, and its specific gravity of 4.5 is exceptional for a nonmetallic mineral, against 2.7 for calcite. Lead minerals like vanadinite and wulfenite feel heavier still.
  • Hardness roughly tracks class. Halides, carbonates and sulfates are soft, while most gem silicates and oxides are hard; the hardness chart gives the numbers.

Building a class-by-class collection from what we stock

A teaching set needs one clean, labeled example per class, and the label matters as much as the stone. Look for listings that name the mineral species rather than a trade name, show the specimen from more than one angle, and state size or weight. Rough or naturally crystallized pieces teach more than polished shapes, because cleavage, habit and luster are what the class differences look like.

  • Pyrite Cluster: the sulfide example. Unpolished natural clusters from Peru, offered from small 1.5 to 2 inch pieces up to extra large, with the brassy metallic luster typical of the class.
  • Halite, Pink: the halide example, from Searles Lake in California per the listing. The listing warns that it dissolves in water, a good reminder that class says nothing about solubility.
  • Optical Calcite: the carbonate example. Cleaved honey and pink pieces show the rhombohedral cleavage that defines the calcite group.
  • Iron Coated Barite: the sulfate example, sold by weight from about 0.29 to 1.07 lb, so you can feel the high specific gravity for yourself.
  • Vanadinite Cluster on Matrix from Mibladen, Morocco: the vanadate example for the phosphate class, a 3.5 inch, 255 g cabinet piece with a known locality.
  • Blue Kyanite: the nesosilicate example, offered as spheres and palm stones. For a teaching tray, a rough blade shows the bladed habit better than a polished shape.

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Frequently asked questions

What are the main mineral classes?

The usual list is native elements, sulfides, halides, oxides and hydroxides, carbonates, sulfates, phosphates and silicates, with borates, nitrates and organic minerals as smaller classes. The Nickel-Strunz scheme numbers them 01 to 10, and Dana splits them into many more numbered classes.

Is quartz a silicate or an oxide?

Both labels appear. The Dana system files quartz as a tectosilicate because its tetrahedra form a three-dimensional framework. The Nickel-Strunz system files it under oxides at 04.DA.05 because its formula is simply SiO2. Most geology courses teach it as a framework silicate.

Which mineral class is the most common?

The silicates. The vast majority of minerals in Earth's crust are silicates, including quartz, feldspar, mica, pyroxene, amphibole, olivine and the clay minerals. Carbonates such as calcite are next in importance in sedimentary rocks like limestone and marble.

Why are the class numbers on two databases different?

They come from two independent systems. Dana numbers have four parts and run up to the silicate classes in the 50s to 70s, while Nickel-Strunz codes start with a two-digit class from 01 to 10 followed by letters. Always note which system a number belongs to.

Do minerals in the same class look alike?

Not necessarily. Halite and fluorite are both halides, yet one dissolves in water and the other does not. Class reflects chemistry, so it predicts some behaviors, such as acid reaction in carbonates, but color and habit vary widely within any class.

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