Triphylite vs lithiophilite
Triphylite vs lithiophilite: one phosphate series, two species, split at 50% iron. Hardness and cleavage match; the sheet analyses read 71.2% vs 6.4% iron.
Triphylite and lithiophilite are one series, LiFe2+(PO4) to LiMn2+(PO4) on the IMA list, and the name changes at 50% iron in iron plus manganese. The sheets’ analyses are 71.2% (triphylite) and 6.4% and 0.3% (lithiophilite). By eye, only colour hints: measured densities meet at 3.50, where a 20.00 g piece reads 14.29 g in water.
In short
- What decides the name. The September 2026 IMA-CNMNC Master List writes triphylite LiFe2+(PO4) and lithiophilite LiMn2+(PO4), and both Handbook of Mineralogy sheets say the two form a series. For a two-atom series, Hatert and Burke (2008) give two names, each running from its end member to the 50 mol.% mark. Iron above half of iron plus manganese is triphylite; below, lithiophilite.
- The 50% line ledger. Worked from each sheet’s oxide analyses on standard atomic weights: the triphylite from “Central Asia” is 71.2% iron of iron plus manganese; the lithiophilite from Buckfield, Maine, 6.4%, and from the Foote mine, North Carolina, 0.3%. Each sits well inside its own name. Both sheets’ ideal columns are the 1:1 composition, exactly on the line.
- The 14.29 g line. Triphylite’s measured density is 3.50 to 3.58 and lithiophilite’s 3.445 to 3.50. A 20.00 g piece reads 14.29 to 14.41 g in water as triphylite and 14.19 to 14.29 g as lithiophilite. The two ranges meet at 14.29 g and the whole span is 0.22 g, so a reading needs a 0.01 g scale and clean, unaltered material.
- Colour is a hint, not a test. Triphylite prints bluish gray to greenish gray. Lithiophilite prints clove-brown, yellowish brown, honey-yellow, salmon-pink, blue-gray and gray. Pink, honey and clove-brown appear only on the lithiophilite sheet; grey-blue is on both; and both turn black from alteration.
- What settles it. An analysis. Refractive indices overlap almost completely and 2V overlaps from 48° to 55°. The X-ray lines differ: the five strongest lithiophilite lines sit 0.8% to 1.4% above their nearest triphylite lines, as its larger cell (2.6% by volume) predicts, but material in the middle of the series falls between.
| Field | Triphylite | Lithiophilite | Do they overlap? | Separates a hand specimen? |
|---|---|---|---|---|
| IMA formula, status, year, country | LiFe2+(PO4); G; 1834; Germany | LiMn2+(PO4); G; 1878; USA | — | Defines the boundary: 50% Fe of Fe + Mn |
| Handbook formula | Li(Fe2+,Mn2+)PO4 | Li(Mn2+,Fe2+)PO4 | Same atoms, order reversed | — |
| Iron share in the sheet’s analyses | 71.2% (“Central Asia”, Russia) | 6.4% (Buckfield, Maine); 0.3% (Foote mine, North Carolina) | No | Only with an analysis |
| Ideal column on the sheet | Li(Fe,Mn)PO4, Mn:Fe = 1:1 | Li(Mn,Fe)PO4, Mn:Fe = 1:1 | Identical figures | No: both are the boundary |
| Density, measured (calc.) | 3.50–3.58 (3.562) | 3.445–3.50 (3.433) | Meet at 3.50 | Only at the ends |
| 20.00 g piece in water | 14.29–14.41 g | 14.19–14.29 g | Meet at 14.29 g | Only at the ends, with a 0.01 g scale |
| Colour as printed | Bluish gray to greenish gray; brownish to black where altered | Clove-brown, yellowish brown, honey-yellow, salmon-pink, blue-gray, gray; surficially black from alteration | Blue-gray and gray on both | Pink, honey or clove-brown point to lithiophilite |
| Streak, lustre | White to grayish white; vitreous to subresinous | White to grayish white; vitreous to subresinous | Identical | No |
| Hardness; cleavage | 4–5; {100} perfect, {010} imperfect, {011} interrupted | 4–5; {100} perfect, {010} good | Yes | No |
| Refractive indices | α 1.675–1.694; β 1.684–1.695; γ 1.685–1.700 | α 1.663–1.696; β 1.667–1.700; γ 1.674–1.702 | Almost completely | No |
| 2V; pleochroism | 0°–55°; none printed | 48°–70°; none to weak, X deep pink, Y pale greenish yellow, Z pale pink | 2V 48°–55° | Only in thin section |
| Cell (Å) and volume | a 6.0285, b 10.3586, c 4.7031; 293.69 Å3 | a 6.094, b 10.427, c 4.743; 301.38 Å3 | Lithiophilite 2.6% larger | Laboratory: X-ray |
| Five strongest X-ray lines (Å) | 3.008, 2.525, 4.277, 3.487, 5.175 | 3.051, 2.548, 4.313, 3.516, 5.236 | Shifted 0.8% to 1.4% | Laboratory, and not in mid-series |
| Alteration products named | Ferrisicklerite, heterosite (deep rose to purple) | Sicklerite, purpurite (reddish purple to deep rose-red) | Both end purple | No |
Is triphylite the same as lithiophilite? One series, two names
Triphylite and lithiophilite are two names in one lithium phosphate series, split by whether iron or manganese is dominant. The September 2026 IMA list writes triphylite as LiFe2+(PO4) and lithiophilite as LiMn2+(PO4). The triphylite sheet writes Li(Fe2+,Mn2+)PO4 and the lithiophilite sheet Li(Mn2+,Fe2+)PO4, and each says it forms a series with the other. Neither IMA row prints the word series; that wording is the Handbook’s.
Where the line falls. Hatert and Burke (2008), Canadian Mineralogist 46, 717–728 describe the simplest case, one atom replacing another at a defined site, as giving “two different mineral names for each compositional range from the end members to the 50 mol.% mark”. Here the two atoms are Fe2+ and Mn2+, so the boundary is iron at half of iron plus manganese. The same paper notes that when three kinds of atom share a site the predominant one names the species; the sheets’ analyses carry magnesium at 0.03 per phosphorus or less, so on them the iron–manganese split is what decides.
The rest of the formula. Lithium, phosphorus and oxygen are the same in both. The end members weigh 157.75 (Fe) and 156.85 (Mn) and are 4.40% and 4.42% lithium; the species facts for the iron member are on triphylite.
The 50% line ledger: what the sheets’ own analyses show
Each sheet’s real analysis sits far from the line, and each sheet’s ideal sits exactly on it. Method: the oxide weights on each sheet were converted to moles on standard atomic weights and iron (FeO plus Fe2O3) taken as a share of iron plus manganese. Triphylite (1), “Central Asia”, Russia: FeO 30.05, Fe2O3 1.07, MnO 12.40, giving 71.2% iron. Lithiophilite (1), Buckfield, Maine: FeO 2.94, MnO 42.58, giving 6.4%. Lithiophilite (2), Foote mine, North Carolina, by electron microprobe with total iron as FeO: FeO 0.16, MnO 46.4, giving 0.3%.
Documented failure: the shared ideal column. The triphylite sheet’s column (2) is Li(Fe, Mn)PO4 with Mn:Fe = 1:1; the lithiophilite sheet’s column (3) is Li(Mn, Fe)PO4 with Mn:Fe = 1:1. Both print P2O5 45.11, FeO 22.84, MnO 22.55 and Li2O 9.50, which our arithmetic reproduces to 0.01. That composition is exactly 50.0% iron, the 50 mol.% mark, so the ideal column on each sheet is the one composition that the rule does not assign to either name. Neither sheet prints its own end member.
Two more readings. The International Gem Society gives specific gravity 3.58 for the pure iron end, 3.52 at Fe:Mn = 1:1 and 3.34 for the pure manganese end, and says density is not linear with the ratio. The 3.34 sits below every lithiophilite figure on its sheet (measured 3.445 to 3.50, calculated 3.433) and below the 3.457 that LiMn2+(PO4) gives in the sheet’s cell; this page prints both and does not resolve them.
Can you tell triphylite from lithiophilite by eye? Mostly not
Only colour and weight give a hint, and both fail in the middle of the series. The lithiophilite sheet prints clove-brown, yellowish brown, honey-yellow and salmon-pink, colours the triphylite sheet does not, so a fresh pink, honey or clove-brown piece is on the lithiophilite side of the sheets. Blue-gray and gray appear on both sheets, and both say the surface goes black from alteration. The International Gem Society triphylite article says the same split in its own words: lithiophilite pinkish to greenish brown, triphylite usually a gray shade of blue or green.
The 14.29 g line. Weighed in water, a 20.00 g piece reads 14.29 to 14.41 g as triphylite and 14.19 to 14.29 g as lithiophilite. The ranges touch at 3.50, the end of one and the start of the other. Above 14.30 g the reading is on the triphylite side, below 14.28 g on the lithiophilite side, and between them it is either. The entire span is 0.22 g, so a kitchen scale cannot read it; the method and the resolution it needs are on how to measure specific gravity at home. The alteration crusts make it worse: ferrisicklerite, heterosite and purpurite are all lighter, 3.2 to 3.4.
What each test is wrong for. Colour is wrong for any blackened or grey piece. Weight is wrong for altered, included or matrix-bound material, and for anything near 3.50. Hardness, cleavage and streak are wrong for this pair altogether: 4 to 5, {100} perfect and white on both. A refractometer is wrong too: triphylite’s α of 1.675 to 1.694 lies inside lithiophilite’s 1.663 to 1.696.
How is triphylite told from lithiophilite in a laboratory?
By chemistry first, and by X-ray as a check. An electron microprobe analysis, the method behind the Foote mine column, gives iron and manganese directly, and the 50% line then names the piece. The X-ray patterns differ in a regular way: lithiophilite’s cell is larger, a 6.094 against 6.0285, b 10.427 against 10.3586, c 4.743 against 4.7031 Å, 2.6% by volume, and its five strongest lines (3.051, 2.548, 4.313, 3.516, 5.236 Å) sit 0.8% to 1.4% above the nearest triphylite lines (3.008, 2.525, 4.277, 3.487, 5.175 Å). Those are the patterns the sheets print, one specimen each (Palermo #1 mine, New Hampshire; Outpost mine, Arizona); a piece in the middle of the series will read between them.
Documented failure: the purple crust. Each species alters along its own chain on the sheets: triphylite to ferrisicklerite and heterosite, which is deep rose to purple with a pale purple streak; lithiophilite to sicklerite and purpurite, which is reddish purple to deep rose-red with a pale purple to pale red streak. A purple rim therefore does not say which primary phosphate it grew on. The lithium-out chain is worked on triphylite.
On a label. “Triphylite-lithiophilite” names the series without placing the piece; if an analysis comes with it, the iron share puts it on one side of the line. The paragenesis of these pegmatite phosphates is on what is mineral paragenesis, and the later manganese phosphates on huréaulite and eosphorite. More guides are in the collecting guides. Nothing on this site is offered for sale; the wanted list is the only commercial route.