Stellerite
Stellerite is a calcium zeolite, density 2.13 and perfect {010} cleavage, in radiating spheres to 12 cm. Its Handbook sheet records no hardness figure at all.
Stellerite is a calcium zeolite, orthorhombic, with perfect {010} cleavage and a measured density of 2.13, forming radiating spheres of colourless to white crystals to 12 cm in altered volcanic rocks. Its Handbook of Mineralogy sheet is one of only four in this site's 158-sheet reference set that records no hardness at all, and its X-ray pattern cannot be distinguished from barrerite.
In short
- Four of 158 sheets in this site's reference set give no hardness figure: stellerite, barrerite, freibergite and cyanotrichite. Stellerite's physical-properties line reads Hardness = n.d. The property most collectors reach for first has simply never been determined on this species.
- Two of those three are the same pair the Handbook says cannot be told apart by X-ray. Stellerite's sheet states its powder pattern cannot be distinguished from barrerite, and barrerite's sheet says the same of stellerite. Both record a measured density of 2.13(1). Two species, no hardness, indistinguishable patterns, identical densities.
- What does separate them is chemistry, and only chemistry. Stellerite is the calcium member and barrerite the sodium-dominant one. Nothing a collector can do at a bench distinguishes them; this is a microprobe determination or an unlabelled specimen.
- Density does separate it from stilbite and heulandite, but barely. Stellerite 2.13, heulandite 2.10 to 2.20, stilbite-Ca 2.19. The whole zeolite group sits within a tenth of a unit, which is why locality and habit carry the identification in practice.
- It is named for a man who died in Siberia in 1746. Georg Wilhelm Steller was the naturalist on Bering's second expedition and the discoverer of the Komandorskiye Islands, where the species was first found. The type material is in the Natural History Museum in London.
| Species | System | Hardness | Density | What separates it |
|---|---|---|---|---|
| Stellerite | Orthorhombic | Not determined | 2.13 | Radiating spheres to 12 cm; calcium-dominant |
| Barrerite | Orthorhombic | Not determined | 2.13 | Sodium-dominant. Nothing else; the powder patterns are indistinguishable |
| Stilbite-Ca | Monoclinic | 3.5 to 4 | 2.19 | The classic sheaf and bowtie habit, and a hardness that has actually been measured |
| Heulandite | Monoclinic | 3.5 to 4 | 2.10 to 2.20 | Coffin-shaped tabular crystals on a pearly {010} cleavage |
| Scolecite | Monoclinic | 5 to 5.5 | 2.25 to 2.29 | Far harder; fine acicular sprays, and it fuses with curling |
| Mesolite | Monoclinic | 5 | 2.26 | Hair-fine needles in dense tufts; harder again |
What n.d. means, and why it is not laziness
The Handbook of Mineralogy prints n.d. — not determined — where a measurement does not exist in the literature. It is a statement about the published record, not about the mineral.
Across the 158 species sheets in this site's reference set, only four carry it in the hardness position: stellerite, barrerite, cyanotrichite and freibergite. Two of the four are zeolites, and the reason is structural. Stellerite grows as radiating spheres of thin crystals that part on a perfect {010} cleavage; there is very little material in a stellerite specimen that can hold a scratch test still. A Mohs determination needs a crystal face big enough and rigid enough to resist a point, and the habit does not supply one.
Freibergite's sheet goes further and records D(meas.) = n.d. as well, so it is the only sheet in the set with neither a hardness nor a measured density. Comparable zeolites do have figures — stilbite-Ca 3.5 to 4, heulandite 3.5 to 4, scolecite 5 to 5.5 — and the sensible working assumption for stellerite is the stilbite range. An assumption is what it is, and this page will not print it as a fact.
The pair the reference literature cannot separate
This is the part worth knowing before buying one.
Stellerite's X-ray powder pattern entry, taken from Villanova Monteleone in Sardinia, ends with the words cannot be distinguished from barrerite. Barrerite's entry, taken from Capo Pula in the same island, ends with the words cannot be distinguished from stellerite. The strongest lines are 9.03 and 9.10, 4.057 and 4.054, 3.028 and 3.028.
Both record a measured density of 2.13(1) — the same figure to the same stated uncertainty. Both record no hardness. Both are orthorhombic, colourless to white, with perfect {010} cleavage. The single property that separates them is which alkali or alkaline-earth cation dominates the channels, calcium in stellerite and sodium in barrerite, and that is a chemical analysis.
The practical consequence: a stellerite specimen without a locality or an analysis is not verifiable, in a stricter sense than usual. The general argument is on whether a specimen without a locality is worth buying, and this species is the sharpest case of it on the site.
Localities, and the Indian material most collectors actually see
The Handbook opens its distribution entry by saying stellerite is increasingly recognised from localities worldwide and that only the best confirmed can be listed — itself a consequence of the identification problem above.
The type occurrence is Copper Island in the Komandorskiye Islands in the Bering Sea, with Klichka in the Chita region of Siberia. Then the Sarbayskaya quarry near Rudniy in Kazakhstan; Villanova Monteleone in Sardinia; Kongsberg in Norway; Ritter Hot Springs in Oregon, Hook Mountain in New York and Fanwood in New Jersey; large crystals from around Gunnedah in New South Wales and from Harcourt, Dookie and Corop in Victoria; and exceptional examples from Cinchwad near Poona and the Nasik district in Maharashtra, India.
The Deccan basalt quarries of Maharashtra are where almost all zeolite specimens in circulation come from, and the same pits produce the heulandite, stilbite, scolecite and apophyllite this site already covers. The Handbook's occurrence line for stellerite — lining cavities and fracture surfaces in volcanic rocks altered by hydrothermal solutions, with zeolites, prehnite and tridymite — describes those quarries exactly.
The type material is held at the Natural History Museum in London under 1934,650. The rest of this reference section is indexed at the species index, and the only commercial route here is the wanted list; there is no catalogue and nothing on this site is offered for sale.