Scapolite
Scapolite is not an IMA species but the group name for the marialite-meionite series: tetragonal, hardness 5 to 6, density 2.50 to 2.78, cleavage {100}, {110}.
Scapolite is not a valid mineral species. It is the group name for a tetragonal series running from marialite, the sodium chloride end, to meionite, the calcium carbonate end, with hardness 5 to 6 and density 2.50 to 2.78 across the two. The September 2026 IMA list has no entry for scapolite; marialite, meionite and silvialite are there.
In short
- Checked two ways, scapolite is not a species. The September 2026 IMA-CNMNC Master List has no entry for it. Marialite (grandfathered, 1866, Italy), meionite (grandfathered, 1801, Italy) and silvialite (approved 1998, Australia) are listed. The Handbook of Mineralogy files both of its sheets under Scapolite group and says most specimens are intermediate in the series.
- Scapolite is feldspar plus salt, and the arithmetic is exact. Three albite, NaAlSi3O8, plus NaCl is marialite, Na4Al3Si9O24Cl; three anorthite, CaAl2Si2O8, plus CaCO3 is meionite, Ca4Al6Si6O24(CO3). The formula masses match to the hundredth: 845.10 and 934.70.
- Density cannot tell scapolite from feldspar; the cleavage geometry can. Marialite is 2.50 to 2.62 against albite's 2.60 to 2.65; meionite 2.74 to 2.78 against anorthite's 2.74 to 2.76. But scapolite cleaves on {100} and {110}, four planes parallel to the prism at 45° intervals.
- Birefringence rises four- to fivefold from one end to the other: 0.007 to 0.009 for marialite, 0.034 to 0.038 for meionite, from the sheets' own refractive indices. It is the one number a refractometer gives that places a scapolite in the series.
- Both sheets say commonly fluoresces — orange to bright yellow or red, under longwave or shortwave or both. They are two of only three sheets in the 176-sheet reference set that use the word commonly for fluorescence; natrolite is the third, and willemite's says typically. The fuller answer is on is scapolite fluorescent.
| Name | Formula | IMA status | Hardness | Density | Birefringence |
|---|---|---|---|---|---|
| Scapolite | Marialite to meionite | Not a species; group name | 5 to 6 | 2.50 to 2.78 | 0.007 to 0.038 |
| Marialite | Na4Al3Si9O24Cl | Valid; grandfathered, 1866, Italy | 5.5 to 6 | 2.50 to 2.62 | 0.007 to 0.009 |
| Meionite | Ca4Al6Si6O24(CO3) | Valid; grandfathered, 1801, Italy | 5 to 6 | 2.74 to 2.78 | 0.034 to 0.038 |
| Silvialite | Ca4Al6Si6O24(SO4) | Valid; approved 1998, Australia | Not in this site's reference set | — | — |
| Albite | NaAlSi3O8 | Valid; grandfathered, 1815, Sweden | 6 to 6.5 | 2.60 to 2.65 | 0.008 to 0.011 |
| Anorthite | CaAl2Si2O8 | Valid; grandfathered, 1823, Italy | 6 to 6.5 | 2.74 to 2.76 | 0.012 to 0.013 |
Is scapolite a mineral species? No, and two sources agree
First check: the IMA list. The September 2026 IMA-CNMNC Master List is the register of valid species. Searching it for scapolite returns nothing. Marialite, Na4Al3Si9O24Cl, is there as a grandfathered species of 1866 from Italy; meionite, Ca4Al6Si6O24(CO3), as a grandfathered species of 1801, also Italy; and silvialite, Ca4Al6Si6O24(SO4), the sulphate analogue of meionite, approved in 1998 from Australia.
Second check: the Handbook. There is no scapolite sheet. Marialite and meionite each have one, each filed under Scapolite group, each recording that it forms a series with the other, and each opening its distribution list with the same warning: most specimens are intermediate in the series. The sheets also record that the two end members crystallise in space group I4/m while intermediate members are P42/n.
This page is filed under scapolite anyway, deliberately. It is the word on the label and the word collectors search for, exactly as with lepidolite, which this site treats the same way. Silvialite has no sheet in this site's 176-sheet reference set, so its physical properties are not given here.
Scapolite is feldspar plus salt, and the arithmetic is exact
The Handbook writes the two formulas in a form that makes the point for you: marialite as 3NaAlSi3O8 · NaCl and meionite as 3CaAl2Si2O8 · CaCO3. The first term in each is three formula units of a plagioclase end member — albite and anorthite respectively.
Check it atom by atom. Three albite is Na3Al3Si9O24; add NaCl and you have Na4Al3Si9O24Cl, the IMA marialite formula exactly. Three anorthite is Ca3Al6Si6O24; add CaCO3 and you have Ca4Al6Si6O24(CO3), the IMA meionite formula exactly. On standard atomic weights the formula masses agree to the hundredth: 845.10 for marialite and 934.70 for meionite, computed both ways. Chlorine is 4.19% of marialite by mass; CO2 is 4.71% of meionite.
This is a composition identity, not a structural one: scapolite is tetragonal and has its own framework, with the chloride or carbonate held in cavities in it. But it explains the two things a collector notices. Scapolite grows where feldspar and a salt-bearing or carbonate-bearing fluid meet — the sheets put it in marbles, calcareous gneisses, granulites, greenschists and skarns — and its densities shadow the feldspars almost exactly.
How to tell scapolite from feldspar
Density will not do it. Marialite measures 2.50 to 2.62 and albite 2.60 to 2.65; meionite 2.74 to 2.78 and anorthite 2.74 to 2.76. The ranges overlap in the first pair and very nearly coincide in the second. Hardness is little better: 5 to 6 against 6 to 6.5.
Habit and cleavage will. Scapolite is tetragonal, in prisms striated parallel to [001] with flat pyramidal terminations, and its distinct cleavages are {100} and {110}. In a tetragonal crystal that is four planes all parallel to the prism axis, the {110} planes lying at exactly 45° to the {100} planes — so cleavage traces run along the length of a broken prism. Feldspars cleave on {001} and {010}, perfect and very good in albite, and tend to break into blocky fragments. The general method is on how to identify feldspar, and the potassium feldspars are on microcline and orthoclase.
A useful negative check: scapolite passes the wide-hardness screen set out on the lepidolite page. Marialite's hardness spans half a point and meionite's one point, so the name problem here does not show in hardness. It shows in the optics.
Which end of the series is my scapolite? Read the birefringence
From the refractive indices on the two sheets: marialite ω 1.539 to 1.550 and ε 1.532 to 1.541, a birefringence of 0.007 to 0.009; meionite ω 1.590 to 1.600 and ε 1.556 to 1.562, a birefringence of 0.034 to 0.038. Both are uniaxial negative. Birefringence rises four- to fivefold across the series.
A decision rule for a refractometer reading, using only the sheets' figures: at or below about 0.009, the stone is consistent with the marialite end; at or above about 0.034, with the meionite end; anywhere between, it is an intermediate member, which the Handbook says most specimens are. An intermediate reading does not name the species: the IMA assigns a name by which end dominates, and that needs an analysis. Note too that the marialite range overlaps albite's 0.008 to 0.011, so birefringence alone does not separate sodic scapolite from albite.
For a label without analysis, the defensible form is scapolite (marialite-meionite series) with the locality. Our note on how to label and catalogue a mineral collection covers adding to an old card without overwriting it.
Where scapolite occurs
Both sheets give the same occurrence: typically regionally metamorphosed rocks, especially marbles, calcareous gneisses, granulites and greenschists; also skarns, some pegmatites, pneumatolytically or hydrothermally altered mafic igneous rocks, and ejected volcanic blocks. Associates are plagioclase, garnet, pyroxenes, amphiboles, apatite, titanite and zircon.
Sodic localities named on the marialite sheet include Pianura near Naples; Slyudyanka near Lake Baikal; Hamburg and Franklin in New Jersey; Bancroft, Ontario, and Bear Lake, Quebec; the La Panchita mine in Oaxaca; Serra da Chibita in Minas Gerais; Tsarasaotra and Betroka in Madagascar; Mpwapwa in Tanzania; and the Mogok district in Myanmar. Calcic localities on the meionite sheet include Monte Somma and Vesuvius, where the analysed specimen came from; the Laacher See in the Eifel; Pargas in Finland; Gooderham, Ontario, and Grenville, Quebec; and Rossie, New York, and Bolton, Massachusetts. Neither sheet names a British locality.
The rest of this reference section is indexed at the species index. We hold no catalogue and nothing here is offered for sale; the wanted list is the only commercial route.