Is hemimorphite the same as larimar
No. Larimar is the trade name of blue pectolite from the Dominican Republic. Both are hardness 4.5 to 5, but density splits them: 3.475 against 2.84 to 2.90.
No. Is hemimorphite larimar? Larimar is a trade name for blue compact pectolite from the Dominican Republic, a sodium calcium silicate; hemimorphite is a zinc silicate. Both are hardness 4.5 to 5, so scratching cannot separate them, but density does: 3.475 for hemimorphite against 2.84 to 2.90 for pectolite. A reading above 3.19 means hemimorphite.
In short
- Larimar is a variety name, not a mineral species. The International Gem Society describes it as blue pectolite from the Dominican Republic, found in 1974. Pectolite, NaCa2Si3O8(OH), is on the IMA list; larimar appears on it 0 times. Hemimorphite is a zinc silicate, Zn4Si2O7(OH)2·H2O, 54.29% zinc.
- Hardness cannot choose. The Handbook of Mineralogy prints 4.5 to 5 for both. A scratch test that separates many look-alikes returns the same answer on these two.
- The 3.19 line. Hemimorphite's measured density is 3.475 and pectolite's 2.84 to 2.90, a gap of at least 19.83%. A 20.00 g piece weighs 14.24 g in water as hemimorphite and 12.96 to 13.10 g as pectolite, at least 1.14 g apart.
- The Handbook's pectolite sheet does not describe larimar. Its colour list is colorless, whitish, grayish and yellowish, with no blue, and its Distribution field does not name the Dominican Republic. The blue variety's facts come from gemmological sources, and this page attributes them.
- Caribbean calcite and blue aragonite are trade names too. Neither appears on the IMA list, and we could not fetch a source we would cite for what they are. If they are the carbonates their names say, calcite is hardness 3 and density 2.7102, and aragonite 3.5 to 4 and 2.95, both lighter and softer than hemimorphite.
| Criterion | Hemimorphite | Pectolite (larimar is its blue variety) | Calcite | Aragonite | Does it choose? |
|---|---|---|---|---|---|
| Formula | Zn4Si2O7(OH)2·H2O | NaCa2Si3O8(OH) | CaCO3 | CaCO3 | Only by analysis |
| Hardness (Mohs) | 4.5 to 5 | 4.5 to 5 | 3 | 3.5 to 4 | Not between hemimorphite and pectolite |
| Density, measured | 3.475 | 2.84 to 2.90 | 2.7102 | 2.95 | Yes: cut-off 3.19 |
| 20.00 g piece, weight in water | 14.24 g | 12.96 to 13.10 g | 12.62 g | 13.22 g | Yes on a 0.01 g scale, on solid material |
| Cleavage | {110} perfect | {100} and {001} perfect | {10-11} perfect: rhombs | {010} distinct | Rarely usable on massive material |
| Colour as recorded | Colorless, white; pale blue, pale green, gray, brown | Colorless, whitish, grayish, yellowish; no blue recorded | Colorless or white, many others | Colorless, white; pale yellow, blue, violet, green, red | No |
| Other recorded properties | Strongly pyroelectric; may fluoresce bluish under SW UV | May be triboluminescent; tough when compact | May fluoresce, SW and LW | Fluorescent red or yellow, LW and SW | Not at home |
| On the IMA list (Sept 2026) | Yes | Yes; larimar is not | Yes | Yes | - |
Is hemimorphite larimar? What larimar actually is
Larimar is not hemimorphite: it is a trade name for blue pectolite, a sodium calcium silicate. The International Gem Society's article, read on 26 September 2026, calls it blue pectolite from the Dominican Republic and says it was found there in 1974; the article illustrates it with material from the Filipinas Larimar Mine, Barahona Province. The IMA-CNMNC list of minerals lists pectolite, NaCa2Si3O8(OH), described in 1828 from Italy. The word larimar does not appear on the list, and neither does Caribbean.
Hemimorphite is a different chemistry altogether. The Handbook of Mineralogy prints Zn4Si2O7(OH)2·H2O, orthorhombic, a secondary mineral of the oxidised zone of zinc deposits. Worked with Zn 65.38, Si 28.085, O 15.999 and H 1.008, the formula mass is 481.71 and the mineral is 54.29% zinc. Pectolite has no zinc. The overlap is the colour: hemimorphite's sheet records pale blue among its colours.
A caution about the source. The Handbook's pectolite sheet, fetched for this page and not part of this site's 176-sheet reference set, lists no blue colour and does not name the Dominican Republic; a search of the text for both returns nothing, while the same search finds its New Jersey locality, Paterson. So the blue variety's facts here are attributed to the gemmological source, not to the Handbook.
Why a scratch test fails and the 3.19 line works
Hemimorphite and pectolite are both hardness 4.5 to 5, so scratching them tells you nothing. The general technique is on how to test mineral hardness properly, but on this pair it will return the same answer twice.
Density separates them by at least 19.83%. Hemimorphite's measured density is 3.475 and pectolite's 2.84 to 2.90. A 20.00 g piece has a volume of 5.76 cm³ as hemimorphite and 6.90 to 7.04 cm³ as pectolite, so it weighs 14.24 g suspended in water against 12.96 to 13.10 g. The midpoint between 2.90 and 3.475 is 3.19. The decision rule: above 3.19, hemimorphite; below it, not hemimorphite, and then pectolite, calcite or aragonite by the other columns of the table. The International Gem Society prints a wider pectolite range, 2.74 to 2.88, which only widens the gap.
Where it fails: botryoidal and fibrous crusts trap air, and a crust on matrix measures the matrix. The method and its limits are on how to measure specific gravity at home, and the same density argument separates hemimorphite from its heavier companion on smithsonite vs hemimorphite.
Is hemimorphite the same as Caribbean calcite or blue aragonite?
Not by name, and we have not verified what those two names are. Both queries sit next to larimar in search suggestions for hemimorphite. Neither Caribbean calcite nor blue aragonite is on the IMA list, and we could not fetch a source we would cite for their composition, so this page does not state it. What it can state is how hemimorphite compares with the two species those names invoke. Calcite is hardness 3 and density 2.7102; aragonite is 3.5 to 4 and 2.95. Both are softer than hemimorphite, so here hardness does help, and both fall below the 3.19 line.
Blue is not rare in the reference set. Of the 176 sheets in this site's reference set, all of which print a colour field, 54 include the word blue, read by case-insensitive regular expression over pdftotext -layout text: hemimorphite, aragonite, smithsonite and turquoise among them. Colour narrows nothing on this page.
Who the answer hemimorphite is wrong for
Who the answer hemimorphite is wrong for: anyone holding a polished blue cabochon with white, cloud-like patterning that reads below 3.19. Who the answer larimar is wrong for: anyone holding sheaf-like or fan-shaped aggregates, thin tabular crystals, or a botryoidal crust from a zinc mine; the hemimorphite sheet names those habits, and localities such as the Ojuela mine, Mapimí and Caldbeck Fells. Who neither suits: glass and ceramic imitations, which exist for larimar and are beyond this page.
The hemimorphite species page covers its colour and the old name calamine; the identification guides are indexed at the collecting guides. Nothing here is offered for sale; the wanted list is the only commercial route.