Is Calcite a Silicate?
Is calcite a silicate? No: calcite, CaCO3, is a carbonate mineral with no silicon, hardness 3, perfect cleavage. Species that are both; why it is not quartz.
No. Calcite is a carbonate, not a silicate: calcium carbonate, Ca(CO3) on the IMA list, 40.04% calcium, 12.00% carbon, 47.96% oxygen and no silicon at all. Silicates are built on silicon-oxygen tetrahedra; calcite on the carbonate ion. Nor is it quartz, SiO2, 46.74% silicon: calcite has hardness 3 against quartz’s 7.
In short
- No silicon, so no silicate. The September 2026 IMA-CNMNC Master List writes calcite Ca(CO3), status G, 1836, country unknown. A script splitting the formula into element symbols returns Ca, C and O. Worked on standard atomic weights, CaCO3 weighs 100.09: 40.04% calcium, 12.00% carbon, 47.96% oxygen, 0% silicon.
- What the word means. An Introduction to Geology (Johnson and others, 2017), chapter 3 says silicate minerals are built around a molecular ion called the silicon-oxygen tetrahedron, and that in calcite one carbon and three oxygen atoms form the carbonate ion. The Handbook of Mineralogy calcite sheet cites Rock-forming minerals, volume 5B, non-silicates.
- The both-groups check. Some minerals are carbonate and silicate at once, and their formulas show both. A script over the IMA list finds 48 parsed rows with a CO3 group and silicon (a raw line scan finds 57, including wrapped rows): spurrite Ca5(SiO4)2(CO3), tilleyite Ca5Si2O7(CO3)2, scawtite Ca7(Si3O9)2(CO3)(H2O)2. Calcite’s formula has the CO3 and not the Si.
- Documented failure: calcium. Calcium is no clue to the class. Calcite is 40.04% calcium, the silicate wollastonite, CaSiO3, 34.50%, and the carbonate-silicate spurrite 45.08%, more than calcite. Read the anion, not the metal.
- Is calcite quartz? No. Quartz is SiO2, 46.74% silicon, hardness 7, density 2.65; calcite is hardness 3, density 2.7102, perfect {10-11} cleavage. The working test is on how to tell calcite from quartz, and is not repeated here.
| Mineral | IMA formula, status | Silicon by mass | CO3 by mass | Calcium by mass | Class | Hardness, density (Handbook) |
|---|---|---|---|---|---|---|
| Calcite | Ca(CO3), G, 1836 | 0% | 59.96% | 40.04% | Carbonate | 3; 2.7102 |
| Aragonite | Ca(CO3), G, 1791 | 0% | 59.96% | 40.04% | Carbonate (polymorph of calcite) | 3.5–4; 2.95 |
| Quartz | SiO2, A, 1967 s.p. | 46.74% | 0% | 0% | Silicate | 7; 2.65 |
| Wollastonite | CaSiO3, A, 1962 s.p. | 24.18% | 0% | 34.50% | Silicate | Not read |
| Spurrite | Ca5(SiO4)2(CO3), G, 1908 | 12.63% | 13.50% | 45.08% | Both groups | Not read |
| Tilleyite | Ca5Si2O7(CO3)2, G, 1933 | 11.50% | 24.56% | 41.02% | Both groups | Not read |
| Scawtite | Ca7(Si3O9)2(CO3)(H2O)2, G, 1930 | 20.23% | 7.20% | 33.68% | Both groups | Not read |
| IMA rows with CO3 and Si | 48 parsed (57 raw lines) | — | — | — | Both groups | Calcite not among them |
Is calcite a silicate or a carbonate? The formula answers it
Calcite is a carbonate: its formula is calcium and the carbonate ion, and has no silicon. The September 2026 IMA list gives calcite as Ca(CO3), status G, 1836, country unknown. The Handbook of Mineralogy calcite sheet writes CaCO3, places it in the calcite group, calls it trimorphous with aragonite and vaterite, and its analysis, from the Monterey Formation, California, reads CaO 53.60, MgO 1.74, FeO 0.43 and CO2 [44.22], calculated from stoichiometry: no SiO2. The sheet’s reference (2) is Chang, Howie and Zussman’s Rock-forming minerals, volume 5B, non-silicates.
The definition, sourced. An Introduction to Geology (Johnson and others, 2017), chapter 3 says silicate minerals are built around a molecular ion called the silicon-oxygen tetrahedron, and that the crystal structure of non-silicate minerals does not contain silica-oxygen tetrahedra. It defines carbonate minerals as salts built around the carbonate ion, and names calcite and dolomite as the two most frequently occurring carbonate minerals. In calcite, it says, one carbon and three oxygen atoms are held together by covalent bonds to form the carbonate ion.
Worked. On standard atomic weights CaCO3 weighs 100.09, of which calcium is 40.04%, carbon 12.00% and oxygen 47.96%; as oxides 56.03% CaO and 43.97% CO2, the sheet’s ideal column. The CO3 group alone is 59.96% of the mass. Silicon is zero. The rest of the species, from crystal forms to localities, is on calcite.
Can a mineral be a carbonate and a silicate? The both-groups check
Yes, and that is the cleanest way to see that calcite is not one. A mineral with both groups writes both in its formula. Method: the IMA list was converted with pdftotext -layout; a row parser read 5,764 rows (the list states 6,239 species), and each formula was tested for the string CO3 and for the element symbol Si. 372 parsed formulas contain CO3, 1,552 contain silicon, and 48 contain both, 27 of them with calcium. A raw scan of every line for CO3 and Si finds 57 lines, the extra being rows the parser misreads or formulas wrapped over two lines; so call it about 50.
Examples from that list. Spurrite, Ca5(SiO4)2(CO3), G, 1908, Mexico: 12.63% silicon and 13.50% CO3 by mass. Tilleyite, Ca5Si2O7(CO3)2, G, 1933, USA: 11.50% silicon. Scawtite, Ca7(Si3O9)2(CO3)(H2O)2, G, 1930, United Kingdom: 20.23% silicon. Meionite, Ca4Al6Si6O24(CO3), G, 1801, Italy, is another. Each has a silicon-oxygen unit and a carbonate in one formula. Calcite, Ca(CO3), has the carbonate and nothing else.
Documented failure: reading the metal. “Calcium” suggests nothing about the class. Calcite is 40.04% calcium; wollastonite, CaSiO3, a calcium silicate on the IMA list, is 34.50%; spurrite is 45.08%, more calcium than calcite, and still a silicate. The anion decides. The same reasoning, same formula but different structure, is what makes calcite and aragonite polymorphs; that test is on is aragonite a polymorph of calcite, and the three Ca(CO3) rows are not counted again here.
Is calcite quartz? Two classes, two formulas
No. Quartz is silicon dioxide, a silicate; calcite is calcium carbonate. The IMA list writes quartz SiO2, status A, 1967 s.p., and the quartz sheet gives hardness 7 and density 2.65 (2.59 to 2.63 when massive). Worked, quartz is 46.74% silicon and 53.26% oxygen; calcite is 0% silicon. The calcite sheet gives hardness 3, density 2.7102(2), perfect {10-11} cleavage and white streak. What makes quartz a mineral, and its SiO2 relatives, are on is quartz a mineral.
Why they get confused. Both are common, colourless to white, and grow together. The calcite sheet lists quartz among its metamorphic associates, with talc, tremolite and grossular, and names calcite a common cement in clastic sedimentary rocks: a calcite-cemented rock can be mostly silicate grains with calcite between them. That is two minerals in one rock, and a label names each. How to separate them on a specimen is on how to tell calcite from quartz and is aragonite the same as calcite; calcite’s luminescence is on is calcite UV reactive.
Is calcite a mineral or a rock? A mineral, with its own IMA row. The calcite sheet calls it a major rock-forming mineral, in limestones, marbles and chalks; Johnson and others call limestone a sedimentary rock built of calcium carbonate. The distinction is on crystal vs mineral: what is the difference. This page gives no acid procedure; the reason is on how to remove calcite from a specimen. More classification questions are in the collecting guides. Nothing on this site is offered for sale; the wanted list is the only commercial route.