Is smithsonite the same as aragonite
No. Smithsonite is zinc carbonate, density 4.43; aragonite is calcium carbonate, 2.95. A 20 g piece weighs 15.49 g or 13.22 g in water. What blue aragonite is.
No. Is smithsonite blue aragonite? No: smithsonite is zinc carbonate, ZnCO3, density 4.43, hardness 4 to 4.5; aragonite is calcium carbonate, CaCO3, density 2.95, hardness 3.5 to 4. Both can be pale blue. A 20.00 g piece weighs 15.49 g in water as smithsonite and 13.22 g as aragonite, which chooses between them.
In short
- Two species, two metals. The September 2026 IMA list records smithsonite, Zn(CO3), and aragonite, Ca(CO3), as separate species. Smithsonite is in the calcite group and hexagonal; aragonite is orthorhombic and gives its name to its own group.
- Colour cannot choose. The Handbook of Mineralogy lists blue on both: smithsonite more rarely blue or bluish gray, aragonite pale shades of blue among others. Both sheets also record reniform and stalactitic forms.
- The 4.3 line. Of the 176 sheets in this site's reference set, 6 have a carbonate formula and blue in the colour field. Only smithsonite measures above 4.3; aragonite and meionite sit below 3.0, and the three copper-bearing carbonates between 3.77 and 4.2.
- Worked: weigh 20.00 g in water. Smithsonite reads 15.49 g, aragonite 13.22 g, calculated as mass times one minus one over density. A 2.27 g gap is 227 steps on a 0.01 g scale.
- Blue aragonite is a description, not a species. It is not on the IMA list. The International Gem Society lists Laurium, Greece, for blue aragonite; the same locality is on the Handbook's smithsonite list. What any piece sold under the name actually is, no source we fetched settles, so the density test is the answer.
| Criterion | Smithsonite | Aragonite | Does it choose? |
|---|---|---|---|
| Formula (Handbook) | ZnCO3 | CaCO3 | Yes, but needs a laboratory |
| Crystal system and group | Hexagonal; calcite group | Orthorhombic, pseudohexagonal; aragonite group | Only on crystals |
| Hardness | 4 to 4.5 | 3.5 to 4 | No: the ranges meet at 4 |
| Density (measured) | 4.43 | 2.95 | Yes: smithsonite is 50.2% denser |
| 20.00 g piece weighed in water | 15.49 g | 13.22 g | Yes: a 2.27 g gap |
| Volume of 20.00 g | 4.51 cm³ | 6.78 cm³ | Yes, by displacement |
| Cleavage | On {10-11}, nearly perfect (rhombohedral) | One distinct, two imperfect | Partly, on a clean break |
| Habit | Typically botryoidal, reniform, spherulitic; crystals uncommon, to 10 cm | Prismatic to acicular crystals to 30 cm; also crusts, globular, reniform, coralloidal, stalactitic | No: both are reniform and stalactitic |
| Blue in the colour field | More rarely blue, bluish gray | Pale shades of blue among others | No |
| Under UV | May fluoresce pale green or pale blue | Fluorescent red or yellow under LW and SW UV, phosphorescent | Only if it glows red or yellow |
| Refractive indices | 1.842 to 1.850 and 1.619 to 1.623 | 1.530, 1.681, 1.685 | Yes, with a refractometer |
Is smithsonite the same as aragonite? The criteria that decide
Smithsonite and aragonite are different species with different metals: zinc carbonate and calcium carbonate. The Handbook of Mineralogy sheet for smithsonite gives ZnCO3, hexagonal, calcite group, hardness 4 to 4.5, measured density 4.43. The Handbook of Mineralogy sheet for aragonite gives CaCO3, orthorhombic and pseudohexagonal, aragonite group, hardness 3.5 to 4, measured density 2.95. The September 2026 IMA list records smithsonite with a United Kingdom type locality, 1832, and aragonite with a Spanish one, 1791.
Criteria in the order they decide: density first, then cleavage, then everything else. Hardness cannot choose, because the ranges meet at 4. Colour cannot, because both sheets list blue. Habit cannot, because both record reniform and stalactitic forms. A good break helps: smithsonite has a nearly perfect rhombohedral cleavage, aragonite one distinct and two imperfect.
Who each answer is wrong for. A density test is wrong for a thin crust on rock, where the matrix dominates the weight; that piece needs a laboratory or a crystal to look at. The UV lamp is wrong as a first test, because only a red or yellow glow points anywhere, towards aragonite, and a dark specimen proves nothing.
The 4.3 line: weighing a blue carbonate
Of the 176 sheets in this site's reference set, 6 have a carbonate group in the formula and blue in the colour field, and only smithsonite measures above 4.3. Method: each sheet's header formula was searched for CO3 (15 sheets), then the colour field for blue. The six, with measured densities: meionite 2.74 to 2.78, aragonite 2.95, azurite 3.773, aurichalcite 3.96, rosasite 4.0 to 4.2, smithsonite 4.43. Meionite is a scapolite silicate carrying carbonate, hardness 5 to 6.
Worked, so you can substitute your own weight. Weight in water is the weight in air times one minus one over the density. A 20.00 g piece reads 20.00 × (1 − 1/4.43) = 15.49 g as smithsonite and 20.00 × (1 − 1/2.95) = 13.22 g as aragonite. At the 4.3 line it would read 15.35 g; at 3.0, 13.33 g. Azurite, aurichalcite and rosasite fall between, at 14.70 to 15.24 g. The method is on how to measure specific gravity at home.
The rule only covers those six. Hemimorphite, the classic blue zinc look-alike, is a silicate of density 3.475 and is not in the list; it is separated from smithsonite on smithsonite vs hemimorphite. Calcite against aragonite, the other half of the confusion, is on is aragonite the same as calcite.
What is blue aragonite? What the sources support
Blue aragonite is not a species name: it does not appear on the IMA list, where aragonite is the species. The aragonite sheet allows pale shades of blue. The International Gem Society aragonite article lists, among notable sources, Greece: Laurium, blue aragonite, and Chile: blue material.
Laurium is on both lists. The Handbook's smithsonite distribution opens abundant at Laurium, Greece, and the International Gem Society smithsonite article says Laurium yields fine blue and green smithsonite crystals. So a Greek locality on a blue carbonate's label does not choose between the two; density does. The district has its own page, Lavrion.
What we do not state. We found no source we would cite for what causes the colour of material sold as blue aragonite, or whether a given piece has been treated, so this page says neither. If the blue is suspiciously even, see how to tell if a crystal is dyed.
Is smithsonite a carbonate, and is it rarer than aragonite?
Smithsonite is a carbonate, ZnCO3, and forms two series, with rhodochrosite and with siderite. Its sheet records it as a secondary mineral of the oxidised zone of zinc-bearing deposits, with associates including hemimorphite, willemite, hydrozincite, cerussite, malachite, azurite, aurichalcite and anglesite. Aragonite's sheet records it as converting to calcite over geologic time and forming in warm marine waters, shells, evaporites, hot springs, caves and blueschist.
Both distribution lines start with many localities. Smithsonite's reads Many localities, even for fine specimens; aragonite's reads Many localities, but fine crystals are uncommon. That is the sheets' own wording, not a market judgement. The species pages are smithsonite and aragonite; the identification guides are indexed at the collecting guides. Nothing on this site is offered for sale; the wanted list is the only commercial route.