The science of oolitic aragonite.
How an ooid is built, the mineralogy that separates aragonite from calcite, and what each measured or reference property does and does not tell a buyer — every figure with its evidence status from TDS-OA-001.
Natural oolitic aragonite, in one view.
Oolitic aragonite is a naturally precipitated, marine-origin calcium carbonate from the Great Bahama Bank.
- Grain
- Rounded, concentrically layered grains — ooids.
- Crystal system
- Orthorhombic aragonite, distinct from the trigonal calcite of quarried limestone.
- Preparation
- Collected, washed, screened and dried; not calcined, milled from rock, or manufactured.
Key facts
- CaCO₃96.17%Representative analysis, ASTM C 25
- Specific gravity2.93Representative analysis
- Mohs hardness3.5–4Published range
- Surface area> 1.7 m²/gRepresentative analysis, Keck Lab
- OriginBahamasGreat Bahama Bank
What the statuses mean
- Representative analysis
- A laboratory result on an identified sample.
- Published range
- A range AragoCor publishes.
- Published reference
- A property of the mineral species from reference data.
None is a guaranteed limit; guaranteed limits are agreed per contract and confirmed per lot by certificate of analysis.
Anatomy of an ooid
Why a sand-sized grain has the surface area of a ground powder.
- NucleusEach ooid grows outward from a nucleus.
- Concentric carbonate layersSuccessive layers of calcium carbonate are laid down in warm, shallow, agitated water.
- Acicular crystals, radialWithin each layer the aragonite forms as acicular crystals, arranged radially.
- Microscopic voidsThe space between those needles is left as microscopic voids.
That internal structure is why the natural grain, unground, has a surface area above 1.7 m²/g (representative analysis, Keck Lab).
The agricultural grade sheet sets that figure against 100-mesh ground limestone (TB-OA-001): the surface area comes from the grain’s architecture rather than from milling. The same structure is behind the higher solubility set out below.
Representative analysis, API RP 56
- Sphericity0.82
- Roundness0.87
Reading these figures
- Surface area is method-dependent and TDS-OA-001 names no method for it, so compare it only against a result by the same method.
- The size of the natural ooids is not the supplied particle distribution of any grade; sizing is stated by grade on the products page.
Mineralogy
The properties, with their status.
Everything below is on TDS-OA-001. The status column says what kind of figure each one is; the note says what it can and cannot be used for.
| Property | Value | Status | What it means |
|---|---|---|---|
| Crystal system | Orthorhombic (XRD) | Representative analysis | The aragonite polymorph, confirmed by X-ray diffraction on the tested sample. |
| Crystal habit | Acicular crystals in concentric ooid layers | Published reference | The structure drawn above; the source of the surface area. |
| Thermal behavior | Metastable; converts to calcite, then to calcium oxide on heating | Published reference | Aragonite reaches a furnace or kiln as calcite. No thermal or energy advantage over limestone is claimed. |
| Decomposition temperature | approx. 825 °C | Published reference | Calcium carbonate decomposes to CaO and CO₂; it does not melt at atmospheric pressure. |
| Specific gravity | 2.93 | Representative analysis | Particle density, against roughly 2.71 for calcite. Not a bulk or bed density, which depends on the delivered cut. |
| Mohs hardness | 3.5–4 | Published range | Harder than calcite at 3. Not an abrasion or equipment-wear claim. |
| Solubility product, 25 °C | 6.0 × 10−9, against 3.36 × 10−9 for calcite | Published reference | Aragonite is the more soluble polymorph at equal conditions. Not a dissolution rate or a neutralizing value; AragoCor publishes neither. |
| Natural buffering point | pH 6.8 | Representative analysis, Keck Lab | Measured on a sample; the test conditions are not published. Dose, chemistry and contact time govern where any water or soil settles. |
| Zeta potential | −6.65 to −33.85 mV | Published range | A negative surface charge. The pH and electrolyte behind the range are not published, so it describes the test conditions as much as the material. |
| Surface area | > 1.7 m2/g | Representative analysis, Keck Lab | Reached in the natural grain size. Method not published; compare like with like. |
| Identity | CaCO₃, molecular weight 100.09, CAS 1317-65-3 | Published reference | Naturally occurring calcium carbonate; not 471-34-1, which is precipitated calcium carbonate. |
Composition by ASTM C 25, Bowser-Morner report 124914A:
- 96.17% CaCO₃
- 38.51% elemental calcium
- MgCO₃ 0.24%
- SrCO₃ 1.43%
- Fe₂O₃ 0.01%
- SiO₂ below 0.01%
The full table, with published ranges for loss on ignition, SO₃, NaCl and moisture, is in TDS-OA-001.
Three properties a buyer can act on — and what each still needs.
Dissolution
The higher solubility product means that at equal particle size and conditions more aragonite dissolves than calcite.
That bears on liming, remineralization and alkalinity buffering.
How much, and how fast, depends on pH, temperature, particle size and contact time, so it is measured on the delivered grade by the method the application uses.
No neutralizing value or dissolution rate is published.
Thermal behavior
Aragonite converts to calcite on heating before either form decomposes at approximately 825 °C, so a glass batch or a kiln receives calcite either way.
That is why no batch or furnace energy reduction is claimed against limestone.
Any thermal effect of the grain form is established in the buyer’s own trial.
The glass brief carries the batch-calculation values.
Grain form and density
Rounded ooids (sphericity 0.82, roundness 0.87) at a particle density of 2.93 flow, pack and settle differently from milled angular rock.
Relevant to packed beds, spreaders, metering and bed weight.
Bulk density, angle of repose and dust depend on the delivered cut and its as-received moisture (5–10%), so they are measured on that cut.
Aragonite vs calcite / GCC
How it differs — where the difference is measurable.
Only rows with a specific figure or a specific structural difference are kept. Calcite values are reference figures for the mineral, not a test of any supplier’s product.
| Property | Oolitic aragonite | Calcite / GCC |
|---|---|---|
| Polymorph | Aragonite, orthorhombic | Calcite, trigonal |
| 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 | 3.36 × 10−9 |
| Grain | Rounded, layered ooids of 50–500 µm, screened from the natural gradation | Milled from quarried rock; shape and size set by the grind |
| Surface area | > 1.7 m2/g in the natural grain size | Product- and grind-dependent |
| On heating | Converts to calcite, then decomposes to CaO | Decomposes to CaO |
| Origin and preparation | Natural marine deposit, Great Bahama Bank; washed, screened, dried; no calcination | Quarried and milled |
The aragonite vs limestone brief carries this comparison with what to test for each row. Market-specific design factors are on the application pages.
The numbers live in the technical data sheets.
TDS-OA-001 carries the full composition, mineralogy, physical properties, screen specification and grade table; one sheet per grade carries the values that apply to it.
Aragonite vs Limestone
Density, hardness, solubility product, grain form and thermal behavior set against calcite, each with its status, and what to test for each.
Read the briefGlass Batch Chemistry with Aragonite
The CaO contribution, loss on ignition, colorants, minor constituents and moisture a batch calculation needs, with the status of each.
Read the briefFrequently asked questions
Both are calcium carbonate, CaCO₃, but they are different mineral polymorphs. Limestone is primarily calcite, which is trigonal; aragonite is orthorhombic, denser (2.93 against about 2.71), harder (Mohs 3.5–4 against 3) and more soluble at equal conditions.
Supplied grades still have to be compared under the conditions of the intended application.
Its solubility product is higher: 6.0 × 10−9 against 3.36 × 10−9 for calcite at 25 °C (published reference). At equal particle size and conditions more aragonite goes into solution.
How fast depends on pH, temperature, particle size and contact time, which is why AragoCor publishes no dissolution rate or neutralizing value and why the comparison is made on the delivered grade by the method the application uses.
No. Calcium carbonate does not melt at atmospheric pressure; it decomposes to calcium oxide and carbon dioxide at approximately 825 °C (published reference).
Aragonite is metastable and converts to calcite on heating before it decomposes, so a furnace receives calcite whichever form was charged. AragoCor claims no thermal or energy advantage over limestone.
Composition is a representative analysis by ASTM C 25 (Bowser-Morner report 124914A) published on TDS-OA-001 with a status against every value.
Per TDS-OA-001 a certificate of analysis is issued for each dispatched lot, and guaranteed limits are agreed in writing per contract rather than inferred from the representative analysis.