measured	value	unit
[SiO₂]	37.2	%
[TiO₂]	0.32	%
[Al₂O₃]	31.2	%
[Cr₂O₃]	0.95	%
[FeO^T]	9.91	%
[NiO]	0.28	%
[MgO]	4.13	%
[Na₂O]	1.88	%

tables:

Table 1-2. Chemical compositions of tourmaline.Elemental abundances are normalized to a total of 100 cg/g of Ota, Tsutomu (2019) Tourmaline in a Mesoarchean pelagic hydrothermal system: Implications for the habitat of early life, Precambrian Research, 334. more