# Borate carbonate

The borate carbonates are mixed anion compounds containing both borate and carbonate ions. Compared to mixed anion compounds containing halides, these are quite rare. They are hard to make, requiring higher temperatures, which are likely to decompose carbonate to carbon dioxide. The reason for the difficulty of formation is that when entering a crystal lattice, the anions have to be correctly located, and correctly oriented. They are also known as carbonatoborates or borocarbonates. Although these compounds have been termed carboborate, that word also refers to the C=B=C$^{5−}$ anion, or CB$_{11}$H$_{12}$$^−$ anion. This last anion should be called 1-carba-closo-dodecaborate or monocarba-closo-dodecaborate.
Some borate carbonates have additional different anions and can be borate carbonate halides or borate carbonate nitrites.

## List

| | chem | mw | crystal system | space group | unit cell | volume | density | comment |
| Qilianshanite | NaHCO$_3$ · H$_3$BO$_3$ · 2H$_2$O | | monoclinic | | a = 16.11 Å, b = 6.92 Å, c = 6.73 Å β = 100.46° | | 1.635 | Biaxial (-) n$_α$ = 1.351 n$_β$ = 1.459 n$_γ$ = 1.486 2V: 50° Max birefringence δ = 0.135 |
| Canavesite | Mg$_2$(HBO$_3$)(CO$_3$) · 5H$_2$O | | monoclinic | | a = 23.49(2) Å, b = 6.16(6) Å, c = 21.91(2) Å β = 114.91(9)° Z=12? | | 1.790 | Biaxial (+) n$_α$ = 1.485 n$_β$ = 1.494 n$_γ$ = 1.505 2V: 86° Max birefringence: δ = 0.020 |
| Potassium bis(carbonato)borate hydrate | K[B(CO$_2$-μ-O-CO$_2$)$_2$]·2H$_2$O | | orthorhombic | Aba2 | a=11.058 b=11.169 c=9.0504 Z=4 | 1117.8 | | spiro at boron |
| | NaK$_{15}$[B$_4$O$_5$(OH)$_4$]$_6$(NO$_2$)$_2$(CO$_3$)·7H$_2$O | 2035.26 | hexagonal | P62c | a=11.1399 c=30.495 Z=2 | 3277.3 | 2.062 | |
| | K$_9$[B$_4$O$_5$(OH)$_4$]$_3$(CO$_3$)OH⋅7 H$_2$O | 1128.82 | | P62c | a=11.207 c=17.193 Z=2 | 1870.2 | 2.005 | |
| | K$_9$[B$_4$O$_5$(OH)$_4$]$_3$(CO$_3$)Cl·7H$_2$O | 1147.29 | hexagonal | P62c | a=11.219 c=17.079 Z=2 | 1861.8 | 2.047 | |
| | K$_9$[B$_4$O$_5$(OH)$_4$]$_3$(CO$_3$)Br·7H$_2$O | 1191.75 | hexagonal | P62c | a=11.243 c=17.132 Z=2 | 1875.4 | 2.110 | |
| | K$_9$[B$_4$O$_5$(OH)$_4$]$_3$(CO$_3$)I⋅7 H$_2$O | 1238.74 | | P62c | a=11.234 c=17.158 Z=2 | 1875.2 | 2.194 | |
| | Ca$_4$(Ca$_{0.7}$Na$_{0.3}$)$_3$(Na$_{0.7}$□ $_{0.3}$)Li$_5$[B $^t$$_{12}$B$^Δ$$_{10}$O$_{36}$(O,OH)$_6$](CO$_3$)(OH) · (OH,H$_2$O) | | | R3 | a=8.99 c=35.91 Z=3 | 2513 | 2.62 | |
| Chiyokoite | Ca$_3$Si(CO$_3$){[B(OH)$_4$]$_{0.5}$(AsO$_3$)$_{0.5}$}(OH)$_6$ · 12H$_2$O | | hexagonal | P6$_3$ | a = 11.0119, c = 10.5252 | 1,105.31 | | |
| Carboborite | Ca$_2$Mg[B(OH)$_4$]$_2$(CO$_3$)$_2$ · 4H$_2$O | | monoclinic | | a = 18.59 Å, b = 6.68 Å, c = 11.32 Å β = 91.68° | | | Biaxial (-) n$_α$ = 1.507 n$_β$ = 1.546 n$_γ$ = 1.569 Max Birefringence: δ = 0.062 |
| Borcarite | Ca$_4$MgB$_4$O$_5$(OH)$_6$(CO$_3$)$_2$ | | monoclinic | C2/m | a=17.840 b=8.380 c=4.445 β =102.04 | 649.906 | 2.790 | Biaxial (-) n$_α$ = 1.590 n$_β$ = 1.651 n$_γ$ = 1.657 2V: 30° Max birefringence: δ = 0.067 |
| Sakhaite | Ca$_3$Mg(BO$_3$)$_2$(CO$_3$)$_2$.(H$_2$O)$_{0.36}$ | | isometric | Fd3m | a = 14.685 Z=4 | 3166.8 | | |
| | Ca$_{12}$Mg$_4$(BO$_3$)$_7$(CO$_3$)$_4$(OH)Cl.H$_2$O | | | Fd3 | | | | |
| Harkerite | Ca$_{12}$Mg$_4$Al(BO$_3$)$_3$(SiO$_4$)$_4$(CO$_3$)$_5$ · H$_2$O | | trigonal | R3m | a = 18.131 Å α = 33.46° | 1614 | | Uniaxial n$_α$ = 1.649 - 1.653 n$_β$ = 1.649 - 1.653 |
| Imayoshiite | Ca$_3$Al(CO$_3$)[B(OH)$_4$](OH)$_6$ · 12H$_2$O | | hexagonal | P6$_3$ | a = 11.026, c = 10.605 | 1,117 | 1.79 | Uniaxial (-) n$_ω$ = 1.497(2) n$_ε$ = 1.470(2) Max birefringence δ = 0.027 |
| Gaudefroyite | Ca$_4$Mn$_3$O$_3$(BO$_3$)$_3$CO$_3$ | | hexagonal | P6$_3$/m | a = 10.6 Å, c = 5.9 Å | 574 | 3.529 | black Uniaxial (+) n$_ω$ = 1.805 - 1.810 n$_ε$ = 2.015 - 2.020 Max Birefringence:δ = 0.210 |
| Numanoite | Ca$_4$Cu(B$_4$O$_6$(OH)$_6$)(CO$_3$)$_2$ | | monoclinic | C2/m | a = 17.794 Å, b = 8.381 Å, c = 4.4494 Å β = 102.42° Z=2 | | | bluish green Biaxial (-) n$_α$=1.618 n$_β$=1.658 n$_γ$=1.672 2V: 60° Max birefringence: δ = 0.054 |
| | Rb$_9$[B$_4$O$_5$(OH)$_4$]$_3$(CO$_3$)Cl⋅7 H$_2$O | 1564.59 | | P62c | a=11.325 c=17.181 Z=2 | 1908.3 | 2.502 | |
| | Rb$_9$[B$_4$O$_5$(OH)$_4$]$_3$(CO$_3$)Br⋅7 H$_2$O | 1609.08 | | P62c | a=11.482 c=17.463 Z=2 | 1993.9 | 2.680 | |
| | Rb$_9$[B$_4$O$_5$(OH)$_4$]$_3$(CO$_3$)I⋅7 H$_2$O | 1656.07 | | P62c | a=11.451 c=17.476 Z=2 | 1984.5 | 2.771 | |
| | NaRb$_3$B$_6$O$_9$(OH)$_3$(HCO$_3$) | | monoclinic | P21 | a = 8.988 Å, b = 8.889 Å, c = 10.068 Å, and β = 114.6° | | | |
| | Sr$_5$(CO$_3$)$_2$(BO$_3$)$_2$ | | orthorhombic | Pnma | a = 7.387 b = 16.556 c = 8.971 Z = 4 | | | UV cut off 190 nm |
| | Sr$_2$CuO$_2$(CO$_3$)$_{0.85}$(BO$_3$)$_{0.15}$ | | | I4 | | | | |
| | Sr(Na$_{0.4}$Sr$_{0.1}$)Na$_2$[B$_5$O$_8$(OH)$_2$] · (CO$_3$)1 − x | | | B2/b | | | | |
| Moydite-(Y) | Y[B(OH)$_4$](CO$_3$) | | orthorhombic | | | | | |
| | K$_6$[Cd$_2$(CO$_3$)$_2$(B$_{12}$O$_{18}$)(OH)$_6$] | 1099.19 | orthorhombic | Pnnm | a=13.0603 b=9.1059 c=12.3860 Z=2 | 1473.0 | 2.478 | colorless |
| | Rb$_6$[Cd$_2$(CO$_3$)$_2$(B$_{12}$O$_{18}$)(OH)$_6$] | 1377.41 | orthorhombic | Pnnm | a=13.3484 b=9.2665 c=12.4946 Z=2 | 1545.5 | 2.960 | colorless |
| | Ba$_2$(BO$_3$)$_{1-x}$(CO$_3$)$_x$Cl$_x$ x=0.1 | | | P3m1 | | | | |
| | Ba$_3$[B$_6$O$_{10}$(OH)$_2$](CO$_3$) | 730.905 | monoclinic | | a=6.5351, b=8.3455, c =11.3489, and β = 98.9568° Z=2 | 611.4 | 3.970 | |
| | Ba$_5$(CO$_3$)$_2$(BO$_3$)$_2$ | 924.34 | orthorhombic | Pnma | a=7.923 b=17.508 c=9.114 Z=4 | 1268.4 | 4.84 | |
| | Ba$_4$Sr(CO$_3$)$_2$(BO$_3$)$_2$ | 874.63 | orthorhombic | Pnma | a=7.731 b=17.349 c=9.048 Z=4 | 1213.6 | 7.787 | |
| | Ba$_6$[B$_{12}$O$_{21}$(OH)$_2$](CO$_3$)$_2$ | 1443.80 | monoclinic | | a =6.5485, b = 19.361, c = 18.120, and β = 90.893° Z=4 | 2297.0 | 4.175 | |
| | Li$_9$BaB$_{15}$O$_{27}$(CO$_3$) | | | P31c | a=8.860, c=15.148 | | | |
| | Ba$_3$(BO$_3$)(CO$_3$)F | 549.84 | trigonal | R3 | a=10.1799 c=18.530 Z=9 | 1663.0 | 4.941 | |
| | Pb$_7$O(OH)$_3$(CO$_3$)$_3$(BO$_3$) | 1756.19 | hexagonal | P6$_3$/mc | a=10.519 c=8.90 Z=2 | 853 | 6.839 | SHG 4.5×KDP |
| Mereheadite | Pb$_{47}$O$_{24}$(OH)$_{13}$Cl$_{25}$(BO$_3$)$_2$(CO$_3$) | | monoclinic | Cm | a = 17.372, b = 27.942, c = 10.6661, β = 93.152$^o$ | 5169.6 | | |
| Britvinite | [Pb$_7$(OH)$_3$F(BO$_3$)$_2$(CO$_3$)][Mg$_{4.5}$(OH)$_3$(Si$_5$O$_{14}$)] | | triclinic | P1 | a = 9.3409, b = 9.3579, c = 18.833 α = 80.365°, β = 75.816°, γ = 59.870° Z=2 | 1378.7 | 5.51 | Biaxial (-) n$_α$ = 1.896 n$_β$ = 1.903 n$_γ$ = 1.903 2V 20° Max birefringence δ = 0.007 |
| Roymillerite | Pb$_{24}$Mg$_9$(Si$_{10}$O$_{28}$)(CO$_3$)$_{10}$(BO$_3$)(SiO$_4$)(OH)$_{13}$O$_5$ | | triclinic | P1 | a = 9.316, b = 9.316, c = 26.463 α = 83.295°, β = 83.308°, γ = 60.023° Z=1 | 1971.2 | 5.973 | Biaxial (-) n$_α$ = 1.860 n$_β$ = 1.940 n$_γ$ = 1.940 2V 5° Max birefringence δ = 0.080 |