Is epidote tourmaline?
No. Epidote is a monoclinic epidote-group silicate, no boron; tourmalines are hexagonal borosilicates. Its lowest index, 1.715, tops schorl, elbaite, dravite.
No. Epidote, Ca2(Al2Fe3+)(Si2O7)(SiO4)O(OH), is a monoclinic epidote-group mineral with no boron; tourmalines such as schorl, elbaite and dravite are hexagonal borosilicates. On the Handbook sheets epidote is biaxial with its lowest index at 1.715, above every index of those three tourmalines (top 1.671), and it has a perfect cleavage where they have very poor ones.
In short
- Two families. The September 2026 IMA-CNMNC Master List gives epidote as Ca2(Al2Fe3+)(Si2O7)(SiO4)O(OH), grandfathered, 1801, and has no row for plain tourmaline. Armbruster et al. (2006) define the epidote group as monoclinic, A2M3[T2O7][TO4](O,F)(OH,O); Henry et al. (2011) call tourmaline an acentric borosilicate, XY3Z6(T6O18)(BO3)3V3W. Worked from the IMA formulas, schorl is 3.08% boron; epidote has none.
- The 1.715 line. Epidote’s lowest index on its Handbook of Mineralogy sheet is α 1.715. The highest index on the schorl, elbaite and dravite sheets is 1.671, so any index of 1.715 or more rules out all three. Across all 11 tourmaline sheets cached here, 9 of 11 sit wholly below 1.715.
- Documented failure: two black tourmalines cross the line. The buergerite sheet (IMA: fluor-buergerite) gives ω 1.735 and the povondraite sheet ω 1.800 to 1.820, inside epidote’s range. Both are uniaxial with yellow-brown or brown streak, so the reading must come with the optic class: the tourmaline sheets give two principal indices, ω and ε, and epidote’s three, α, β and γ. Schorl and elbaite may show slight biaxiality under strain, so that call needs a clean grain.
- In the hand. Epidote has a perfect cleavage on {001}; the three tourmaline sheets print very poor. A 20.00 g piece reads 14.08 to 14.27 g in water as epidote and 13.10 to 13.79 g as schorl, elbaite or dravite, a 0.29 g gap at the closest. Hardness, 6 to 7 against 7, does not separate them, and both are striated prisms.
- Pleochroic, and found together. Yes, epidote is pleochroic: strong, colourless to pale yellow or green, greenish yellow and yellowish green for X, Y and Z. Schorl and dravite are very strongly pleochroic too, so pleochroism alone does not decide. The schorl and dravite sheets both list epidote among their associates, so the two can share a specimen.
| Criterion | Epidote | Schorl | Elbaite | Dravite | Does it separate? |
|---|---|---|---|---|---|
| Family (source) | Epidote group (Armbruster et al. 2006) | Tourmaline supergroup (Henry et al. 2011) | Tourmaline supergroup | Tourmaline supergroup | Yes, on paper |
| Boron by mass | 0 | 3.08% | 3.46% | 3.38% | Yes, by analysis |
| Crystal system | Monoclinic | Hexagonal, 3m | Hexagonal, 3m | Hexagonal, 3m | Yes, by optics or X-ray |
| Optic class | Biaxial (−) | Uniaxial (−) | Uniaxial (−) | Uniaxial (−) | Yes, on a clean grain |
| Refractive indices | α 1.715–1.751, γ 1.734–1.797 | ω 1.660–1.671, ε 1.635–1.650 | ω 1.633–1.651, ε 1.615–1.630 | ω 1.634–1.661, ε 1.612–1.632 | Yes: the 1.715 line, gap 0.044 |
| Birefringence | 0.019–0.046 | 0.021–0.025 | 0.018–0.021 | 0.022–0.029 | No |
| Cleavage | Perfect {001}, imperfect {100} | Very poor | Very poor | Very poor | Yes, if a cleavage face shows |
| Hardness | 6–7 | 7 | 7 | 7 | No |
| Density | 3.38–3.49 | 3.18–3.22 | 2.90–3.10 | 3.03–3.18 | Yes, narrowly |
| 20.00 g in water | 14.08–14.27 g | 13.71–13.79 g | 13.10–13.55 g | 13.40–13.71 g | Yes: 0.29 g at the closest |
| Pleochroism | Strong; X, Y, Z | Very strong; O, E | O, E (no strength given) | Very strong; O, E | No |
| Colour (sheet) | Pistachio-green to pale green, yellow, greenish black | Black, brownish black, bluish black | Green, blue, red, orange, yellow, colourless | Brown to black, red, yellow, blue, green, colourless, white | No |
Is epidote a type of tourmaline? No: two different families
The formulas. The September 2026 IMA list writes epidote Ca2(Al2Fe3+)(Si2O7)(SiO4)O(OH), status G, 1801; the Handbook epidote sheet writes Ca2Al2(Fe3+,Al)(SiO4)(Si2O7)O(OH), epidote group, forming a series with clinozoisite. The list’s tourmaline rows include schorl, NaFe2+3Al6(Si6O18)(BO3)3(OH)3(OH); elbaite, Na(Al1.5Li1.5)Al6(Si6O18)(BO3)3(OH)3(OH); and dravite, NaMg3Al6(Si6O18)(BO3)3(OH)3(OH). Every tourmaline formula carries (BO3)3; epidote’s carries no boron. Worked on standard atomic weights, boron is 3.08% of schorl, 3.46% of elbaite and 3.38% of dravite.
The nomenclature reports. Armbruster et al. 2006, Recommended nomenclature of epidote-group minerals (European Journal of Mineralogy 18, 551) say epidote-group minerals are monoclinic, with topology consistent with space group P21/m and the general formula A2M3[T2O7][TO4](O,F)(OH,O). Henry et al. 2011, Nomenclature of the tourmaline-supergroup minerals (American Mineralogist 96, 895) call tourmaline a crystallographically acentric borosilicate with the generalised formula XY3Z6(T6O18)(BO3)3V3W. How many tourmaline species there are, and why a label should read tourmaline without an analysis, is on tourmaline and is schorl black tourmaline; why epidote is not a pyroxene either is on is epidote a pyroxene. This page does not repeat those tests.
The 1.715 line: one refractometer reading
The rule. The epidote sheet gives α 1.715 to 1.751, β 1.725 to 1.784, γ 1.734 to 1.797, biaxial (−). The schorl sheet gives ω 1.660 to 1.671 and ε 1.635 to 1.650; elbaite 1.633 to 1.651 and 1.615 to 1.630; dravite 1.634 to 1.661 and 1.612 to 1.632. Epidote’s lowest printed index, 1.715, is 0.044 above the highest of the three tourmalines, and no index on the four sheets falls between 1.671 and 1.715. Any index of 1.715 or more rules out schorl, elbaite and dravite.
Checked across the cached set. Eleven tourmaline-group sheets are cached here: schorl, elbaite, dravite, uvite, fluor-schorl, oxy-schorl, foitite, feruvite, liddicoatite, buergerite and povondraite. A script compared each sheet’s highest printed index with 1.715. Nine sit wholly below it; feruvite comes closest at 1.687. The method for reading a stone on the instrument is on how to tell if tourmaline is real.
Where the line fails, documented
Two dark tourmalines. The buergerite sheet, filed under the name the IMA list now gives as fluor-buergerite, prints ω 1.735 and ε 1.655, dark brown to almost black with a yellow-brown streak and a distinct prismatic cleavage. The povondraite sheet prints ω 1.800 to 1.820 and ε 1.743 to 1.751, black, brown streak, nearly opaque. Both readings fall inside epidote’s range, and buergerite’s distinct cleavage weakens the cleavage test too. Both sheets say uniaxial, so the optic class, determined on a clean grain, still separates them from biaxial epidote; this page gives no instrument technique.
Strain and weight. The schorl and elbaite sheets add that under strain they may show slight biaxiality, so a single strained grain can mislead. Density is narrower than it looks: the highest measured density among the tourmaline sheets here, buergerite’s 3.31, reads 13.96 g in water for 20.00 g against epidote’s lowest 14.08 g, a gap of 0.125 g worked on the unrounded values, too narrow to lean on; the method and its limits are on how to measure specific gravity at home.
Is epidote pleochroic? Yes, and so is tourmaline
The sheets. Epidote: Pleochroism strong; X colourless, pale yellow or pale green; Y greenish yellow; Z yellowish green: three directions. Schorl: very strong; O yellow-brown; E pale yellow or pale brown. Dravite: very strong; O pale yellow; E colourless, yellowish, greenish or brownish. Elbaite: O pink, pale green or pale to deep blue; E colourless, yellow, olive-green or purplish, with no strength given. The tourmaline sheets list two colours, O and E; the epidote sheet three, X, Y and Z. Strength alone does not choose: both families are recorded as strongly pleochroic.
Colour and habit overlap. Epidote is pistachio-green to pale green, yellow, yellowish green, greenish yellow or greenish black; elbaite and dravite include green, and schorl is black. Epidote’s crystals are prismatic, to 35 cm, elongated and striated parallel to [010]; the tourmalines are striated parallel to [0001], schorl and elbaite with a prominent trigonal prism, dravite with cross sections typically triangular with curved convex sides. A rounded triangular cross section points to tourmaline; a perfect cleavage in a green prism points to epidote. Other tourmaline confusions are on is tourmaline a quartz.
Epidote and tourmaline together
The association lines. The schorl sheet lists epidote among its associates, with quartz, albite, microcline, orthoclase, garnet, muscovite, topaz, cassiterite, scheelite, fluorite and beryl; the dravite sheet lists it with quartz, calcite, dolomite, microcline, albite, muscovite, fluorite and titanite. A green-and-black specimen may therefore carry both, and each crystal needs its own reading. The epidote sheet’s occurrence is regionally metamorphosed rocks, contact zones and altered plagioclase; schorl’s is granites, granite pegmatites, high-temperature veins and some metamorphic rocks.
Where to go next. The species pages are epidote and tourmaline; the sheet numbers on this page are quoted directly and agree with is epidote a pyroxene (14.08 to 14.27 g) and is schorl black tourmaline (13.71 to 13.79 g). More identification guides are in the collecting guides. We hold no catalogue and nothing here is offered for sale; the wanted list is the only commercial route.