Microlite
Microlite is no longer a species but a group name: 12 tantalum-dominant pyrochlore-supergroup minerals on the IMA list. How to read an old microlite label.
Microlite is no longer a species but a group name: since 2013 it names the tantalum-dominant group of the pyrochlore supergroup. Twelve rows on the September 2026 IMA list end in -microlite. An old microlite label means a cubic tantalum oxide from granite pegmatite, hardness about 4 to 5, density 6.16 to 6.6, species undetermined.
In short
- No mineral called plain microlite is on the September 2026 IMA-CNMNC Master List. In 2013 Christy and Atencio allocated betafite, elsmoreite, microlite, pyrochlore and roméite as group names within the pyrochlore supergroup. Twelve rows on the list end in -microlite: 9 approved and 3 redefined in 2010. A label reading microlite is a group determination.
- The group is defined by one site. The general formula is A2B2X6Y. In the microlite group B is tantalum; in the pyrochlore group it is niobium; in the roméite group, pentavalent antimony. All 12 microlite rows carry Ta in the formula, and none of the pyrochlore rows does.
- The name is built from two prefixes. The first gives the dominant anion at Y (fluor-, hydroxy-, oxy-, or hydro- for water), the second the dominant cation at A (calcio-, natro-, plumbo- and so on; keno- means vacant). Fluorcalciomicrolite is fluorine at Y and calcium at A.
- Worked tantalum test on the Handbook analyses: Ta/(Ta+Nb) at the B site is 0.929 to 0.973 in the four microlite-group analyses, and 0.000 and 0.070 in the two pyrochlore analyses. The densities follow: 6.160 to 6.6 for the microlite-group sheets, 4.33 to 4.90 for pyrochlore.
- None of the 176 sheets in this site's reference set mentions microlite or pyrochlore, and no header formula in the set contains tantalum or niobium (script search). The figures here come from the two microlite-group sheets, the pyrochlore sheet and the IMA list.
| IMA name | IMA formula | Status | IMA No. / year | Type country | Y site (first prefix) | A site (second prefix) |
|---|---|---|---|---|---|---|
| Fluorcalciomicrolite | (Ca,Na,☐)2Ta2O6F | A | 2012-036 | Brazil | F | Ca |
| Fluornatromicrolite | (Na1.5Bi0.5)Ta2O6F | A | 1998-018 | Brazil | F | Na |
| Hydrokenomicrolite | (☐,H2O)2Ta2(O,OH)6(H2O) | A | 2011-103 | Brazil | H2O | Vacancy |
| Hydroxycalciomicrolite | Ca1.5Ta2O6(OH) | A | 2013-073 | Brazil | OH | Ca |
| Hydroxykenomicrolite | (☐,Na,Sb3+)2Ta2O6(OH) | Rd | 2010 s.p. | Russia | OH | Vacancy |
| Kenomicrolite | ☐2Ta2[O4(OH)2]☐ | A | 2024-097 | Brazil | One prefix only; formula shows ☐ at Y | ☐ at A in the formula |
| Kenoplumbomicrolite | (Pb,☐)2Ta2O6[☐,(OH),O] | A | 2015-007a | Russia | Vacancy | Pb |
| Oxybismutomicrolite | (Bi1.33☐0.67)Ta2O6O | A | 2019-047 | Russia | O | Bi |
| Oxycalciomicrolite | Ca2Ta2O7 | A | 2019-110 | Brazil | O | Ca |
| Oxynatromicrolite | (Na,Ca,U)2(Ta,Nb)2O6(O,F) | A | 2013-063 | China | O | Na |
| Oxystannomicrolite | Sn2Ta2O6O | Rd | 2010 s.p. | Finland | O | Sn |
| Oxystibiomicrolite | (Sb3+,Ca)2Ta2O6O | Rd | 2010 s.p. | Sweden | O | Sb3+ |
Is microlite a mineral? Not since 2013: it is a group name
First check: the IMA list. The September 2026 IMA-CNMNC Master List has no row for microlite. Twelve names end in it, set out in the table. Nine are approved species with IMA numbers from 1998-018 to 2024-097, and three are marked Rd, redefined, 2010 s.p.: hydroxykenomicrolite, oxystannomicrolite and oxystibiomicrolite. For all three the list’s second reference is Canadian Mineralogist 48 (2010), 673. The Handbook’s hydroxykenomicrolite sheet gives that paper in full: Atencio, Andrade, Christy, Gieré and Kartashov, The pyrochlore supergroup of minerals: nomenclature.
Second check: the published rulings. Christy and Atencio’s 2013 clarification, in Mineralogical Magazine 77, 13–20, allocated microlite, with betafite, elsmoreite, pyrochlore and roméite, as group names within the pyrochlore supergroup. Atencio’s 2021 update says the 2010 system replaced Hogarth’s of 1977. It names seven species that were valid when the 2010 system came in, and three of them are the three redefined microlite rows. The list has grown since: kenomicrolite, the newest, is IMA 2024-097.
This page is filed under microlite deliberately, because that is the word on older labels. The axinite and scapolite pages treat their group names the same way. There is no Handbook sheet called microlite; the two microlite-group sheets used here, fluorcalciomicrolite and hydroxykenomicrolite, are not in this site’s 176-sheet reference set. Nor is the pyrochlore sheet used for comparison.
How a microlite-group name is built, with a worked example
The rule, from Atencio’s 2021 summary: a name is two prefixes and a root, and the root is the group name. The first prefix gives the dominant anion at the Y site, or water or a vacancy; the second gives the dominant cation at the A site, or water or a vacancy. The group is fixed by B: tantalum for microlite, niobium for pyrochlore, Sb5+ for roméite, tungsten for elsmoreite.
Worked on the Handbook fluorcalciomicrolite sheet. Its analysis of Volta Grande pegmatite material recalculates to (Ca1.07Na0.81☐0.12)(Ta1.84Nb0.14Sn0.02)[O5.93(OH)0.07][F0.79(OH)0.21]. B is Ta 1.84 of 2, so the root is microlite. At A, calcium 1.07 beats sodium 0.81, so the second prefix is calcio. At Y, fluorine 0.79 beats hydroxyl 0.21, so the first is fluor. The result is fluorcalciomicrolite, IMA 2012-036.
Several old names map to current ones, per Atencio 2021. Cesstibtantite (1981) is now hydroxykenomicrolite, and the Handbook sheet says the same. Sukulaite is oxystannomicrolite, and stibiomicrolite is oxystibiomicrolite. The discredited parabariomicrolite corresponds to the trigonal 3R polytype of hydrokenomicrolite. Name endings across the whole IMA list are counted on why do mineral names end in -ite.
Microlite or pyrochlore? The tantalum test, worked
Tantalum against niobium at the B site decides it. Converting each Handbook analysis from oxide weight per cent to atoms (Ta2O5 441.89 and Nb2O5 265.81 on standard atomic weights, two metal atoms each) gives Ta/(Ta+Nb):
- Fluorcalciomicrolite, Volta Grande, Brazil: Ta2O5 76.02%, Nb2O5 3.47% → 0.929, matching the sheet’s own Ta1.84 Nb0.14.
- Hydroxykenomicrolite, Kola Peninsula, two analyses: 0.950 and 0.938. Tanco pegmatite, Manitoba: 0.973.
- Pyrochlore, Oka, Quebec: Nb2O5 65.8%, Ta2O5 0.04% → 0.000. Hybla, Ontario: 0.070.
Density follows the chemistry. The tantalum atom weighs 1.95 times the niobium atom, and the sheets show it: fluorcalciomicrolite 6.160 calculated, hydroxykenomicrolite 6.4 to 6.6 measured. Pyrochlore is 4.33 calculated for CaNaNb2O6F, and its sheet prints the measured value as 4.45 to 4.90 if uranoan. That is three sheets, not a survey, so treat it as a clue rather than a rule; see how to measure specific gravity at home. The Handbook pyrochlore sheet was written under the older scheme. It says pyrochlore forms a series with microlite and requires Nb above Ta at B, which is the same boundary.
Fluorescence is not a group property. The hydroxykenomicrolite sheet records yellow-orange to orange under longwave UV. The 2013 description of fluorcalciomicrolite says it does not fluoresce under ultraviolet light. Background is on fluorescent minerals explained.
How to read an old microlite label
Read it as “a tantalum-dominant pyrochlore-supergroup mineral, species not determined”. The species name needs two further determinations, the dominant A cation and the dominant Y anion, and neither can be made by eye. All twelve rows share tantalum at B; they differ only at A and Y. The honest current label is microlite group with the locality; how to label and catalogue a mineral collection covers the form.
Which species is it likely to be? No source we fetched reassigns old microlite material as a whole, so we do not name one. What the sources allow is this. The Handbook pyrochlore sheet, written under the older scheme, requires sodium plus calcium above 20% of the A site and puts pyrochlore in a series with microlite. Read that way, the old name most plausibly points to one of the five calcium- or sodium-dominant members: fluorcalciomicrolite, fluornatromicrolite, hydroxycalciomicrolite, oxycalciomicrolite or oxynatromicrolite. That is our reading, not a published reassignment. The vacancy-, lead-, tin-, bismuth- and antimony-dominant members exist too.
Where the two Handbook sheets place the group: granite pegmatites. They name the Volta Grande pegmatite, Nazareno, Minas Gerais, Brazil, and the Harding pegmatite, New Mexico, for fluorcalciomicrolite. For hydroxykenomicrolite they name the Leshaia pegmatite in the Vuoriyarvi complex, Kola Peninsula, Russia; Dobrá Voda, Velké Meziříčí, Czech Republic; the Tanco pegmatite, Bernic Lake, Manitoba; and near Mt. Holland, Western Australia. Fluorcalciomicrolite’s associates include microcline, albite, quartz, muscovite, spodumene, cassiterite, fluorite and beryl, with lepidolite in quotation marks as the sheet prints it; see lepidolite and cassiterite. The rest of the reference section is at the species index. We hold no catalogue and nothing here is offered for sale; the wanted list is the only commercial route.