Serandite
Serandite is NaMn2Si3O8(OH): triclinic, rose-red to black, hardness 5–5.5, density 3.34, crystals to 20 cm, large at Mont Saint-Hilaire. The three-row ladder.
Serandite is NaMn2+2Si3O8(OH) on the September 2026 IMA list: a triclinic sodium manganese silicate, rose-red, orange, pink, brown or black, hardness 5–5.5, density 3.34, crystals to 20 cm, large at Mont Saint-Hilaire, Quebec. It is the manganese end of a three-row ladder with schizolite and pectolite; its Handbook analyses carry 1.51 and 1.90 Mn per formula.
In short
- The species. The Handbook of Mineralogy sheet, headed Sérandite, gives triclinic prismatic to acicular crystals elongated along [010], or bladed, blocky or tabular on {100}, to 20 cm, and radiating aggregates; perfect {001} and {100} cleavage; hardness 5–5.5; density 3.34; rose-red, orange, salmon-pink, light pink, colourless, brown or black; white streak. The September 2026 IMA-CNMNC Master List row reads NaMn2+2Si3O8(OH), status Rn, 1931, Guinea.
- The three-row ladder. By script, the IMA list has three rows of the form NaM2Si3O8(OH): pectolite NaCa2, schizolite NaCaMn and serandite NaMn2, with 0, 1 and 2 manganese. Recast to 3 Si, the sheet’s Rouma Isle analysis carries 1.51 Mn and 0.69 Ca, and its Tanohata mine analysis 1.90 Mn and 0.17 Ca. Grice et al. (2019) give the schizolite cotypes 0.68 Mn and 1.11 Ca.
- Documented failure: the ladder needs X-rays. The Rouma Isle analysis, from the island of Lacroix’s 1931 description, sits between schizolite’s 1 Mn and serandite’s 2. Grice et al. separated schizolite from its neighbours with single-crystal and powder X-ray diffraction, not with an analysis alone, and no source fetched here states a compositional boundary, so this page draws none.
- Documented failure: the 3.42 check. The sheet’s triclinic cell holds 347.3 ų. Two formula units of NaMn2Si3O8(OH), 362.12 g/mol, give 3.463; the Tanohata formula gives 3.460. Neither reproduces the printed calculated 3.42, and the measured 3.34 is lower again. Pectolite’s own cell, worked the same way, gives 2.875 against its printed [2.87]. This page quotes the measured 3.34.
- Where it is found. The Distribution field names Rouma Isle, Los Islands, Guinea; Point of Rocks, New Mexico; the Gem mine, San Benito Co., California; Granite Mountain near Little Rock, Arkansas; large crystals from Mont Saint-Hilaire and from near Saint-Amable, Quebec; the Tanohata mine, Japan; and the Tumannoe deposit and Mt. Karnasurt, Russia. Hazard questions about any mineral are routed to toxic minerals in a collection; nothing here is health or safety advice.
| Formula or analysis | Source | Mn per 3 Si | Ca per 3 Si | Mn share | Density (measured) | 20.00 g in water | Name the source gives |
|---|---|---|---|---|---|---|---|
| NaCa2Si3O8(OH) | IMA pectolite row (G, 1828, Italy) | 0 | 2 | 0 | 2.84–2.90 (pectolite sheet) | 12.96–13.10 g | Pectolite |
| Thetford mines, Quebec | Pectolite sheet, analysis | 0 | 1.98 | 0 | — | — | Pectolite |
| NaCaMnSi3O8(OH) | IMA schizolite row (Rn, 2013-067, South Africa) | 1 | 1 | 0.50 | — | — | Schizolite |
| Schizolite cotypes, South Greenland (mean) | Grice et al. 2019, abstract | 0.68 (+ 0.12 Fe) | 1.11 | 0.38 | — | — | Schizolite |
| Rouma Isle, Guinea | Serandite sheet, analysis (1) | 1.51 | 0.69 | 0.69 | — | — | Serandite |
| Tanohata mine, Japan (microprobe) | Serandite sheet, analysis (2) | 1.90 | 0.17 | 0.92 | — | — | Serandite |
| NaMn2+2Si3O8(OH) | IMA serandite row (Rn, 1931, Guinea) | 2 | 0 | 1.00 | 3.34 (serandite sheet) | 14.01 g | Serandite |
What is serandite? A sodium manganese silicate
Serandite is NaMn2+2Si3O8(OH): sodium, two manganese, three silicon, eight oxygen and one hydroxyl, in a triclinic structure. The Handbook of Mineralogy serandite sheet, headed with the older spelling Sérandite, writes Na(Mn2+,Ca)2Si3O8(OH) and describes prismatic to acicular crystals elongated along [010], or bladed, blocky or tabular crystals flattened on {100}, to 20 cm, as well as radiating aggregates and massive material. Twins form around [010] with composition plane {100}, and less commonly as contact twins by reflection on {110}.
Physical properties, as printed. Cleavage perfect on {001} and {100}; fracture uneven; brittle; hardness 5–5.5; density 3.34 measured and 3.42 calculated. Transparent to translucent; rose-red, orange, salmon-pink, light pink, colourless, brown or black, colourless in thin section; streak white; lustre vitreous to greasy, with fibrous aggregates dull to silky. Biaxial (+), α = 1.668, β = 1.671, γ = 1.703, 2V = 39°. The method for the hardness figure is on how to test mineral hardness properly.
What the lists record. The September 2026 IMA-CNMNC Master List gives serandite as NaMn2+2Si3O8(OH), status Rn, which its legend defines as a mineral renamed during the IMA era, year 1931, country Guinea. The sheet names it for J.M. Sérand, who aided the collection of type material, and puts the type material at the National Museum of Natural History, Washington, D.C., catalogue 96515. It marks no type locality, so this page names none (what a type locality is). On standard atomic weights the formula weighs 362.12 g/mol: 30.34% manganese, or 39.18% MnO, the figure the pectolite page also works.
Serandite, schizolite or pectolite? The three-row ladder
The IMA list has three species in this series, not two: pectolite NaCa2Si3O8(OH), schizolite NaCaMnSi3O8(OH) and serandite NaMn2+2Si3O8(OH). A script over the list for formulas of the form NaM2Si3O8(OH) finds exactly these three rows. Both Handbook sheets say pectolite and serandite form a series; the schizolite row, status Rn with number 2013-067, cites Grice et al. (2019), Mineralogical Magazine 83, 473 as its first reference. That abstract says the name marshallsussmanite, approved as IMA2013-067, was discredited in favour of the older name schizolite, which Winther described in 1901 from Tutop Agtakôrfia in the Ilímaussaq complex, South Greenland. The IMA row gives South Africa as the country; the abstract gives the Greenland type locality. Both are printed here because the two sources differ.
The ladder, worked. Recast to three silicon, the sheet’s Rouma Isle, Guinea analysis (MnO 28.99, CaO 10.42) carries 1.51 Mn and 0.69 Ca; its Tanohata mine, Japan microprobe analysis (MnO 37.33, CaO 2.62) carries 1.90 Mn and 0.17 Ca, close to the sheet’s own formula line, Mn 1.88, Ca 0.17. As a share of manganese plus calcium that is 0.69 and 0.92, the figures the pectolite page also gives. The schizolite cotypes in Grice et al. average Na1.00Ca1.11Mn0.68Fe0.12Si3.041O8(OH): a share of 0.38.
Documented failure: chemistry does not name the rung. The sheet’s Rouma Isle analysis comes from the island of Lacroix’s 1931 paper describing serandite, the first reference the IMA list gives (Comptes Rendus 192), yet with 1.51 Mn it sits between schizolite’s 1 and serandite’s 2. Grice et al. identified schizolite by single-crystal and powder X-ray diffraction and optical properties, and no source fetched for this page states where one name stops and the next begins. A pink NaMSi3O8(OH) silicate from an old label is therefore serandite only as far as its label and a structural determination say so; this page does not re-identify the Rouma Isle material.
How dense is serandite? Documented failure: the 3.42 check
The sheet prints a measured density of 3.34 and a calculated density of 3.42, and neither matches the 3.46 its own cell gives. The triclinic cell, a = 7.683, b = 6.889, c = 6.747 Å, α = 90.53°, β = 94.12°, γ = 102.75°, read from the rendered sheet, holds 347.3 ų. Two formula units of NaMn2Si3O8(OH) give 2 × 362.12 ÷ (0.60221 × 347.3) = 3.463. The Tanohata formula, Na1.00(Mn1.88Ca0.17Mg0.01)Si2.97O8(OH), gives 3.460. Pectolite’s sheet cell, worked the same way with NaCa2Si3O8(OH), gives 2.875 against its printed [2.87], so the method reproduces there.
On the balance. At the measured 3.34 a 20.00 g piece reads 14.01 g in water; at the printed 3.42 it would read 14.15 g. Pectolite reads 12.96–13.10 g, at least 0.91 g lighter. Bustamite, (Mn2+,Ca)3Si3O9 on its sheet, reads 13.98–14.17 g at 3.32–3.43, overlapping serandite completely, and rhodonite 14.40–14.68 g at 3.57–3.76. The method is on how to measure specific gravity at home.
The pink manganese minerals. Where the balance fails, hardness and cleavage help. Serandite is 5–5.5 with two perfect cleavages, {001} and {100}; bustamite and rhodonite are 5.5–6.5 on their sheets; rhodochrosite, Mn(CO3), is 3.5–4 with perfect rhombohedral cleavage. The rhodochrosite sheet names large twinned crystals at Mont Saint-Hilaire, a serandite locality too. The pectolite sheet records no colour beyond colourless, whitish, greyish and yellowish. Rhodonite against rhodochrosite is on is rhodochrosite the same as rhodonite.
Where is serandite found? Mont Saint-Hilaire and the sheet’s list
The sheet’s Distribution, as printed. From Rouma Isle, Los Islands, Guinea. In the USA, at Point of Rocks, Colfax Co., New Mexico; from the Gem mine, San Benito Co., California; on Granite Mountain, near Little Rock, Pulaski Co., Arkansas. Large crystals from Mont Saint-Hilaire, and from near Saint-Amable, Quebec, Canada. In the Tanohata mine, Iwate Prefecture, Japan. At the Tumannoe deposit, Bol’shoi Santar Island, Okhotsk Sea, and on Mt. Karnasurt, Lovozero massif, Kola Peninsula, Russia. We add no other locality.
Mont Saint-Hilaire. The sheet’s X-ray powder pattern is from Mont Saint-Hilaire, and its Occurrence field places serandite there in sodalite xenoliths and pegmatites cutting syenites and nepheline syenites in an intrusive alkalic gabbro-syenite complex, with analcime, aegirine, mangan-neptunite and microcline. Elsewhere it occurs in vugs in phonolite (Point of Rocks) and in a contact-metamorphosed manganese deposit (Tumannoe). At Rouma Isle its associates include sodalite, nepheline, astrophyllite, arfvedsonite, eudialyte, leucophanite, villiaumite and fluorite. The sheet does not mark Mont Saint-Hilaire, or anywhere else, as the type locality.
Shared places. Three place names appear on both the serandite and pectolite sheets: Mont Saint-Hilaire, Granite Mountain near Little Rock, and the Lovozero massif. The pectolite page’s natrolite comparison is not repeated here; nor is the Larimar material, which is on is hemimorphite the same as larimar. More species are in the species index. We hold no catalogue and nothing here is offered for sale; the wanted list is the only commercial route.