Ammonioborite mineral

Grandfathered hydrated ammonium pentaborate mineral with current September 2026 IMA-CNMNC approved formula (NH4)3B15O20(OH)8(H2O)4, status G, and original-description year 1933 (not a numbered IMA approval CURIE). Schaller (1933) described ammonioborite from the boric-acid fumaroles (soffioni) of Larderello, Tuscany, Italy, on specimens in the US National Museum (including USNM 93756, 94172, and Roebling R6167) intergrown with sassolite (boric acid, B(OH)3). Utilizing the faster dissolution of sassolite in cold water (0.2 g artificial sassolite dissolved in 75 mL cold water within 15 min, whereas ammonioborite required more than 2 h), Schaller isolated 93 mg of purified ammonioborite for wet-chemical titration (Table 5, p. 488: (NH4)2O 9.78 wt%, B2O3 74.18 wt%, H2O by difference 16.04 wt%), proposing the oxide ratio (NH4)2O·5B2O3·5H2O (equivalent to (NH4)2B10O16·5H2O) and distinguishing it from larderellite by optical refractive indices (alpha = 1.470, beta = 1.487, gamma = 1.540) and Posnjak's X-ray powder photographs (Figure 2, p. 490). Schaller reported that laboratory crystallization trials from aqueous boric- acid and ammonia solutions at room temperature yielded only the orthorhombic synthetic 1:5:8 hydrate (NH4)2O·5B2O3·8H2O and failed to synthesize ammonioborite. The later crystal-structure determination by Merlino and Sartori (Science 171 (1971), 377), which established the current polyborate formula (NH4)3B15O20(OH)8(H2O)4 (oxide ratio 3(NH4)2O·15B2O3·16H2O, i.e. 1:5:5.33), is cited in the IMA Master List but is behind a paywall and was not independently acquired at curation. Distinct from larderellite, sassolite, elemental boron, and borate commodities; no criticality designation, microbial mechanism, or industrial recovery yield is asserted.

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Record source: data/records/ammonioborite.yaml