Aragonite vs Limestone: a comparative technical analysis

The measured and reference properties that separate natural oolitic aragonite from calcite limestone, with the status of each, and what a buyer has to test rather than assume.

Summary

Aragonite and calcite share the formula CaCO₃ and are distinct mineral polymorphs. Every AragoCor figure below carries its evidence status from TDS-OA-001: Representative analysis describes a tested sample, Published range a range AragoCor publishes, and Published reference a property of the mineral species. None is a guaranteed limit. Calcite values are reference figures for the mineral, not a test of any supplier’s product.

Side-by-side: the properties that differ

Side-by-side: the properties that differ
Property	AragoCor oolitic aragonite	Status	Calcite / limestone
Crystal system	Orthorhombic (XRD)	Representative analysis	Trigonal / rhombohedral
Crystal habit	Acicular crystals in concentric ooid layers	Published reference	Deposit- and milling-dependent
Specific gravity	2.93	Representative analysis	Approximately 2.71
Mohs hardness	3.5–4	Published range	3
Solubility product, 25 °C	6.0 × 10⁻⁹	Published reference	3.36 × 10⁻⁹
Grain	Rounded ooids, 50–500 µm; sphericity 0.82, roundness 0.87 (API RP 56)	Published range / Representative analysis	Milled rock; deposit- and milling-dependent
Surface area	> 1.7 m²/g in the natural grain size	Representative analysis	Product- and grind-dependent
Thermal behaviour	Metastable: converts to calcite, then decomposes to CaO at approx. 825 °C	Published reference	Stable form; decomposes to CaO
Composition	96.17% CaCO₃, ASTM C 25	Representative analysis	Product- and deposit-dependent
Origin and preparation	Natural Bahamian marine deposit; collected, washed, screened, dried; no calcination	Published reference	Quarried and milled; deposit-dependent

Solubility products, decomposition temperature and calcite values are properties of the mineral species from published reference data, not tests of AragoCor material. Surface area and the buffering point on TDS-OA-001 are published without test method or conditions; compare them only against a result obtained by the same method.

What each difference means, and what to test

Dissolution

Aragonite has the higher solubility product, so at equal particle size and under the same conditions more of it dissolves. Whether that matters is set by pH, temperature, particle size and contact time. Measure it on the delivered grade by the method the application uses: a liming determination for soil, a contactor test for water. AragoCor publishes no neutralizing value and no dissolution rate.

Density and hardness

A specific gravity of 2.93 against about 2.71 changes volume per tonne, settling and bed weight. Mohs 3.5–4 against 3 bears on attrition in handling. Neither is an abrasion or equipment-wear claim; measure wear where it matters.

Thermal behaviour

Aragonite converts to calcite on heating before either form decomposes, so both reach a furnace or kiln as calcite. No thermal or energy advantage is claimed against limestone; any effect is established in the buyer’s own batch or kiln trial.

Morphology and flow

Rounded ooids of 50–500 µm flow, pack and meter differently from milled angular rock. Bulk density, angle of repose and dust behaviour depend on the delivered cut and its moisture (5–10% as received), so measure them on that cut.

Surface area

> 1.7 m²/g is reached in the natural grain size, without grinding. The method is not published, and a BET result and a permeametry result are not comparable, so set it against a competitor figure only when the method matches.

Chemistry

96.17% CaCO₃ and 38.51% elemental calcium are representative analysis of one sample. MgCO₃ is 0.24%: a calcium source, not a magnesium source. SrCO₃ at 1.43% is the largest non-calcium carbonate present and residual NaCl is 0.06–0.25%; disclose both where a specification limits them.

Application selection path

Application selection path
Step	Design focus
1. Define requirements	Set chemistry, particle distribution, moisture, handling and regulatory limits for the application.
2. Match material properties	Compare crystal form, density, morphology, composition and particle distribution against the table above.
3. Set process conditions	Align dosage, pH, temperature, residence time, equipment and formulation, then test the delivered grade.
4. Define commercial fit	Align grade, packaging, volume, destination and acceptance criteria; guaranteed limits are agreed per contract and confirmed per lot by certificate of analysis.

Conclusion

Natural oolitic aragonite and calcite limestone are different crystal forms of calcium carbonate with measurably different density, hardness, solubility, grain form and thermal behaviour. The figures above say what the material is; only a test under the intended conditions says what it does in a given application. The full composition and physical properties are in TDS-OA-001.

Technical Brief TB-OA-002 · Rev B · September 2026 · © AragoCor Minerals LLC · info@aragocorminerals.com · +1 (209) 487-0110