Nonsilicate Minerals: Carbonates, Oxides, Sulfides

Silicates own the crust by volume, but the minerals that supply our metals, salt, and building stone come from the other families. Meet the carbonates, oxides, sulfides, sulfates, halides, and native elements.

Uni Year 1Earth science
⏱️ About 16 min
Nonsilicate Minerals: Carbonates, Oxides, Sulfides — illustration
Illustrative image (AI-generated).

Silicon and oxygen dominate the crust, so silicates get top billing. But flip through the minerals that built human civilisation — the iron in a bridge, the copper in a wire, the salt on your dinner, the gold in a ring, the limestone in a cathedral — and almost none of them are silicates. The non-silicate families are rare in the crust yet extraordinarily useful, and geologists know them by the single anion that defines each group.

💡
The big idea: Non-silicate minerals are classified by their characteristic <strong>anion</strong> — the negatively charged ion or element at their core. <strong>Carbonates</strong> (CO₃²⁻), <strong>oxides</strong> (O²⁻), <strong>sulfides</strong> (S²⁻), <strong>sulfates</strong> (SO₄²⁻), <strong>halides</strong> (Cl⁻, F⁻), and <strong>native elements</strong> (a pure element) each have a diagnostic chemistry, a few common examples, and a use. Knowing the anion tells you the group at a glance.
🎯 By the end, you'll be able to
  • Identify the major non-silicate mineral groups by their characteristic anion or element
  • Give a common example and an economic or everyday use for each non-silicate group
  • Distinguish a sulfide (S²⁻, e.g. pyrite FeS₂) from a sulfate (SO₄²⁻, e.g. gypsum)
  • Explain how native elements such as gold and copper occur as pure substances
📎 Helpful to know first

Sorted by their anion

Silicates are unified by one anion (the SiO₄ tetrahedron). The non-silicates are instead a set of smaller families, each built around a different anion. Identify the anion and you have the group:

  • Carbonates — CO₃²⁻
  • Oxides — O²⁻
  • Sulfides — S²⁻
  • Sulfates — SO₄²⁻
  • Halides — Cl⁻, F⁻
  • Native elements — a pure element (Au, Cu, C, S)

Although these make up only a small slice of the crust, they supply most of our metals, salt, fertiliser, plaster, and building stone.

The major non-silicate mineral groups grouped by anion, with an example mineral and use for each Carbonates anion: CO₃ 2 minus Calcite — CaCO₃ limestone, marble, cement; fizzes in acid Oxides anion: O 2 minus Hematite — Fe₂O₃ iron ore; red rust pigment. Also magnetite Sulfides anion: S 2 minus Pyrite — FeS₂ ore of many metals (Cu, Pb, Zn); NOT a sulfate Sulfates anion: SO₄ 2 minus Gypsum — CaSO₄·2H₂O plaster, drywall; evaporates in dry seas Halides anion: Cl minus, F minus Halite — NaCl rock salt; also fluorite (CaF₂) Native elements a single element Gold — Au metals (Au, Cu), diamond (C), sulfur (S) Non-silicate minerals — grouped by their anion Though rare in the crust, these groups supply most of our metals, salt, and building stone.
Six non-silicate families, each defined by its anion. The two most-confused — sulfide and sulfate — sit side by side; telling them apart is the key skill below.

Carbonates — the CO₃²⁻ minerals

Carbonates are built around the carbonate anion, CO₃²⁻. The two you will meet constantly are calcite (CaCO₃) and dolomite (CaMg(CO₃)₂). They are the minerals of limestone and marble, the raw material for cement, and the stuff of seashells and coral reefs. Carbonates form wherever carbon dioxide, water, and calcium meet — warm shallow seas are the great carbonate factories of the planet.

✨ The acid test: calcite fizzes
Drop weak acid (dilute hydrochloric acid, or even vinegar on a fresh surface) on calcite and it fizzes — the carbonate reacts to release carbon dioxide gas. That fizz is the fastest field test in all of mineralogy: it identifies calcite (and limestone) on the spot and distinguishes it from look-alikes such as quartz.

Oxides — the metal ores

Oxides pair a metal with oxygen (O²⁻). Many of our most important ores are oxides: hematite (Fe₂O₃) and magnetite (Fe₃O₄) supply iron; corundum (Al₂O₃) is the abrasive on sandpaper and, with trace impurities, the gems ruby (red, chromium) and sapphire (blue, iron + titanium). Magnetite is also naturally magnetic — it was the first compass.

Sulfides — the metal source, and fool's gold

Sulfides combine a metal with sulfur as S²⁻ (no oxygen involved). Pyrite (FeS₂) is the shiny, brass-colored fool's gold, but the economically vital sulfides are the ores of copper (chalcopyrite), lead (galena), and zinc (sphalerite). Sulfides are the main source of many metals — and, when weathered at old mines, the source of acid drainage, a hazard we revisit in Module 10.

⚠️ Don't confuse sulfide (S²⁻) with sulfate (SO₄²⁻)
The two names differ by one letter and trip up nearly every beginner. A sulfide bonds a metal to plain sulfur (S²⁻) — pyrite is FeS₂, galena is PbS, no oxygen. A sulfate bonds a metal to the sulfate anion (SO₄²⁻), which does contain oxygen — gypsum is CaSO₄·2H₂O. The '-ide' ending means a single element (sulfur alone); the '-ate' ending means oxygen is part of the anion. Pyrite and gypsum sit on opposite sides of that line.

Sulfates, halides, and native elements

Sulfates (SO₄²⁻) include gypsum (CaSO₄·2H₂O), mined for plaster and drywall, and formed when seawater evaporates in arid basins. Halides pair a metal with a halogen ion: halite (NaCl) is rock salt, and fluorite (CaF₂) feeds the fluoride in toothpaste and steelmaking. Native elements are minerals made of a single element: gold (Au), copper (Cu), diamond and graphite (both C), and sulfur (S). Metals like gold occur native because they are chemically unreactive — they stay pure while other elements combine.

📝 Worked example: Classify each mineral into its non-silicate group and give the tell: (a) pyrite FeS₂, (b) gypsum CaSO₄·2H₂O, (c) gold Au.
  1. (a) Pyrite FeS₂ — sulfide. Iron bonded to sulfur (S²⁻) with no oxygen in the formula. The '-ide' suffix and the missing oxygen mark a sulfide.
  2. (b) Gypsum CaSO₄·2H₂O — sulfate. Calcium bonded to the sulfate anion SO₄²⁻, which contains oxygen. The '-ate' suffix and the oxygen mark a sulfate.
  3. (c) Gold Au — native element. A single element with no anion at all; gold is unreactive enough to occur pure.
✓ Pyrite is a sulfide (metal + S²⁻), gypsum is a sulfate (metal + SO₄²⁻, with oxygen), and gold is a native element (a pure element).

Check your understanding

1. Calcite (CaCO₃) belongs to which mineral group?
Calcite contains the carbonate anion CO₃²⁻, so it is a carbonate — the mineral of limestone, marble, and seashells, and it fizzes in acid.
2. What is the key difference between a sulfide and a sulfate?
A sulfide (e.g. pyrite FeS₂) has sulfur but no oxygen; a sulfate (e.g. gypsum CaSO₄·2H₂O) has the SO₄²⁻ anion, which includes oxygen. The '-ide' vs '-ate' ending signals the difference.
3. Gold (Au) and copper (Cu) can occur as pure metals. Which group are they?
Minerals made of a single element are native elements. Gold and copper are unreactive enough to be found pure, as are diamond and graphite (C) and sulfur (S).
4. Why are oxides like hematite and magnetite economically important?
Hematite (Fe₂O₃) and magnetite (Fe₃O₄) are the principal iron ores; the metal extracted from them is the foundation of steel and modern construction.
🔎 Related lessons
Previous: The Silicates Next: Hardness, Cleavage, Luster (identifying minerals) Ore Deposits & Mineral Resources (M10)
✅ Key takeaways
  • Non-silicate minerals are grouped by their characteristic anion: carbonates (CO₃²⁻), oxides (O²⁻), sulfides (S²⁻), sulfates (SO₄²⁻), halides (Cl⁻/F⁻), and native elements.
  • Carbonates (calcite, dolomite) make limestone and cement and fizz in acid; oxides (hematite, magnetite) supply iron; sulfides (pyrite, galena) supply metals.
  • Sulfides bond a metal to plain sulfur (no oxygen); sulfates bond a metal to SO₄²⁻ (with oxygen) — a one-letter name difference that means different chemistry.
  • Halides include halite (rock salt) and fluorite; sulfates include gypsum (plaster).
  • Native elements (gold, copper, diamond, graphite, sulfur) are minerals of a single pure element, found uncombined because they are chemically unreactive.
➡️ You now know what the major minerals are and how they are built. The last skill in this module is the one every field geologist uses first: picking up an unknown specimen and reading its hardness, cleavage, luster, and streak to put a name to it.
Want to test yourself on this? Try the Science practice tests →
🎓 Go deeper: university courses & trusted references

Handpicked external material for this module — for when you want the full university treatment of minerals.

External sites are listed for reference only. This course is independent and has no affiliation with, or endorsement from, the institutions named.