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(NH4)2[B5O6(OH)4]2 · H2O
White; colourless in ...
In allusion to the composition, containing AMMONIum and being a BORate.
Dimorph of:
Microscopic plates, grouped in parallel; commonly as fine-grained granular masses.

Classification of Ammonioborite

Approved, 'Grandfathered' (first described prior to 1959)

E : Pentaborates
A : Neso-pentaborates

5 : Pentaborates

9 : Borates
1 : Borates of the alkalis and boric acid

Physical Properties of Ammonioborite

Diaphaneity (Transparency):
White; colourless in transmitted light
None Observed
1.765(4) g/cm3 (Measured)    1.76 g/cm3 (Calculated)

Optical Data of Ammonioborite

Biaxial (+)
RI values:
nα = 1.470 nβ = 1.487 nγ = 1.540
Measured: 60° , Calculated: 62°
Max Birefringence:
δ = 0.070
Image shows birefringence interference colour range (at 30µm thickness) and does not take into account mineral colouration.
Surface Relief:
relatively weak

Chemical Properties of Ammonioborite

(NH4)2[B5O6(OH)4]2 · H2O
IMA Formula:
(NH4)3B15O20(OH)8 · 4H2O
Elements listed in formula:

Crystallography of Ammonioborite

Crystal System:
Class (H-M):
2/m - Prismatic
Space Group:
Cell Parameters:
a = 25.27 Å, b = 9.65 Å, c = 11.56 Å
β = 94.29°
a:b:c = 2.619 : 1 : 1.198
Unit Cell Volume:
V 2,811.07 ų (Calculated from Unit Cell)
Compact, fine-grained masses. Partially as platy microscopic crystals, frequently grouped in parallel position.

Type Occurrence of Ammonioborite

Place of Conservation of Type Material:
National Museum of Natural History, Washington, D.C., USA, 93756, 94172, R6167.
Geological Setting of Type Material:
Boric acid fumaroles in a volcanic region. In boric acid-rich fumarolic lagoons.
Associated Minerals at Type Locality:

Relationship of Ammonioborite to other Species

6.EA.05SborgiteNa[B5O6(OH)4] · 3H2O
6.EA.05LeucostauritePb2[B5O9]Cl · 0.5H2O
6.EA.10SantiteK[B5O6(OH)4] · 2H2O
6.EA.10Ramanite-(Rb)Rb[B5O6(OH)4] · 2H2O
6.EA.10Ramanite-(Cs)Cs[B5O6(OH)4] · 2H2O
6.EA.25UlexiteNaCa[B5O6(OH)6] · 5H2O
9.1.4BiringucciteNa2B5O8(OH) · H2O
9.1.5NasiniteNa2[B5O8(OH)] · 2H2O
9.1.6KerniteNa2[B4O6(OH)2] · 3H2O
9.1.7EzcurriteNa4B10O17 · 7H2O
9.1.8TincalconiteNa2(B4O7) · 5H2O
9.1.9BoraxNa2(B4O5)(OH)4 · 8H2O
9.1.11SborgiteNa[B5O6(OH)4] · 3H2O
9.1.12AristarainiteNa2MgB12O20 · 8H2O
9.1.13SantiteK[B5O6(OH)4] · 2H2O
9.1.14Larderellite(NH4)B5O7(OH)2 · H2O

Other Names for Ammonioborite

Name in Other Languages:

Other Information

Other Information:
Slowly and completely soluble in cold water.
Health Risks:
No information on health risks for this material has been entered into the database. You should always treat mineral specimens with care.

References for Ammonioborite

Reference List:
Sborgi and Meccacci (1916) Reale accademia nazionale dei Lincei, Rome, Att.: 25: 455.

Schaller, W.T. (1931) Ammonioborite, a new mineral. in: Proceedings of the eleventh annual meeting of the Mineralogical Society of America at Toronto, Canada. American Mineralogist: 16: 107-119.

D'Achiardi (1932) Periodico de Mineralogia-Roma: 3: 36.

Schaller, W.T. (1933) Ammonioborite, a new mineral. American Mineralogist: 18: 480-492.

Palache, C., Berman, H., Frondel, C. (1951) The System of Mineralogy of James Dwight Dana and Edward Salisbury Dana, Yale University 1837-1892, Volume II. John Wiley and Sons, Inc., New York, 7th edition, revised and enlarged: 366-367.

Clark, J.R., Christ, C.L. (1959) Studies of borate minerals (VII): X-Ray studies of ammonioborite, larderellite, and the potassium and ammonium pentaborate tetrahydrates. American Mineralogist: 44: 1150-1158.

Merlino, S., Sartori, F. (1971) Ammonioborite: New borate polyion and its structure. Science: 171: 377-379.

Anderson, J.E., Bubnova, R.S., Filatov, S.K., Ugolkov, V.L., Britvin, S.N. (2009) Thermal investigation of ammonioborite (NH4)3[B15O20(OH)8]•4H2O. Glass Physics and Chemistry: 35: 191-198.

Internet Links for Ammonioborite URL:
Please feel free to link to this page.

Localities for Ammonioborite

This map shows a selection of localities that have latitude and longitude coordinates recorded. Click on the symbol to view information about a locality. The symbol next to localities in the list can be used to jump to that position on the map.
(TL) indicates type locality for a valid mineral species. (FRL) indicates first recorded locality for everything else. ? indicates mineral may be doubtful at this locality. All other localities listed without reference should be considered as uncertain and unproven until references can be found.
Italy (TL)
  • Tuscany
    • Pisa Province
      • Pomarance
D'Achiardi G. (1932): Considerazioni e ricerche sulla larderellite, ammonioborite (?) e bechilite (?) di Larderello (Pisa). Periodico di Mineralogia - Roma pp. 36-42; Palache, C., Berman, H., & Frondel, C. (1951), The System of Mineralogy of James Dwight Dana and Edward Salisbury Dana, Yale University 1837-1892, Volume II: 366.
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