# Arsenate arsenite

An arsenate arsenite is a chemical compound or salt that contains arsenate and arsenite anions (AsO$_3$$^{3-}$ and AsO$_4$$^{3-}$). These are mixed anion compounds or mixed valence compounds. Some have third anions. Most known substances are minerals, but a few artificial arsenate arsenite compounds have been made. Many of the minerals are in the Hematolite Group.
An arsenate arsenite compound may also be called an arsenite arsenate.

## Properties

Some members of this group of materials like mcgovernite has an extremely high unit cell dimension of 204 Å.

## Related

Mixed valence pnictide compounds related to the arsenate arsenites include the nitrite nitrates, and phosphate phosphites.

## List

| name | formula | ratio AsO$_4$:AsO$_3$ | system | space group | unit cell Å | volume | density | properties |
| Arsenic dioxide | AsO$_2$ | 1:1 | orthorhomnic | Pnma | a=8.597 b=5.235 c=7.269 Z=8 | 327.1 | 4.382 | |
| Arsenic(III) Arsenic(V) Oxide Hydroxide | As$_3$O$_5$(OH) | 1:2 | monoclinic | P2$_1$/c | a = 12.504 b = 4.593 c = 10.976 β = 118.08° Z = 4 | 556.2 | 3.84 | |
| | H$_6$As$^{3+}$$_7$As$^{5+}$$_7$O$_{31}$ | 1:1 | hexagonal | P6$_3$ | a = 12.0525 c = 4.7344 Z = 2 | 595.6 | | |
| Segerstromite | Ca$_3$(As$^{5+}$O$_4$)$_2$[As$^{3+}$(OH)$_3$]$_2$ | 2:1 | cubic | I2$_1$3 | a = 10.7627 Z = 4 | 1246.71 | 3.46 | colourless; refract index: n = 1.731 |
| Synadelphite | Mn$^{2+}$$_9$(As$^{5+}$O$_4$)$_2$(As$^{3+}$O$_3$)(OH)$_9$ · 2H$_2$O | 2:1 | Orthorhombic | Pnma | a = 10.75 b = 18.86c = 9.88 Z=4 | 2005 | 3.58 | red; Biaxial (+); refract index: n$_α$ = 1.750 - 1.870 n$_β$ = 1.751 - 1.880 n$_γ$ = 1.761 - 1.930 |
| Hematolite | (Mn,Mg,Al,Fe$^{3+}$)$_{15}$(As$^{5+}$O$_4$)$_2$(As$^{3+}$O$_3$)(OH)$_{23}$ | 2:1 | trigonal | R3 | a = 8.275 Å, c = 36.60 Å Z=3 | 2,170.4 | 3.49 | deep red; Uniaxial (-) refractive index n$_ω$ = 1.733 n$_ε$ = 1.714; Birefringence: 0.019 |
| Turtmannite | (Mn,Mg)$_{22.5}$Mg$_{3-3x}$((V$^{5+}$,As$^{5+}$)O$_4$)$_3$(As$^{3+}$O$_3$)$_x$(SiO$_4$)$_3$O$_{5-5x}$(OH)$_{20+x}$ | | trigonal | | a = 8.259 c = 204.3 Z=12 | 12,068 | 3.8 | light yellow; Uniaxial (-); refractive index: n$_ε$ = 1.787 |
| Carlfrancisite | Mn$^{2+}$$_3$(Mn$^{2+}$,Mg,Fe$^{3+}$,Al)$_{42}$[As$^{3+}$O$_3$]$_2$(As$^{5+}$O$_4$)$_4$[(Si,As$^{5+}$)O$_4$]$_6$[(As$^{5+}$,Si)O$_4$]$_2$(OH)$_{42}$ | | trigonal | R3c | a = 8.2238 c = 205.113 Z=6 | 12,013.5 | 3.620 | yellow-orange; Uniaxial (+) refractive index: n$_ω$ = 1.756(2) n$_ε$ = 1.758 Birefringence: δ = 0.002 |
| | K$_2$Cu$_3$(As$_2$O$_6$)$_2$ | 1:1 | monoclinic | C2m | a=10.359 b=5.388 c=11.234 β=110.48° | | | [As(V)As(III)O$_6$]$^{4−}$ |
| Dixenite | CuMn$^{2+}$$_{14}$Fe$^{2+}$(SiO$_4$)$_2$(As$^{5+}$O$_4$)(As$^{3+}$O$_3$)$_5$(OH)$_6$ | 1:5 | trigonal | R3 | a = 8.233 c = 37.499 Z=3 | 2201 | 4.35 | deep red-brown; Uniaxial (+) refractive index n$_ω$ = 1.970 n$_ε$ = 1.730 |
| Arakiite | (Zn,Mn$^{2+}$)(Mn$^{2+}$,Mg)$_{12}$(Fe$^{3+}$,Al)$_2$(As$^{5+}$O$_4$)$_2$(As$^{3+}$O$_3$)(OH)$_{23}$ | 2:1 | monoclinic | Cc | a = 14.248 b = 8.228 c = 24.23 β = 93.62° Z=4 | 2843 | 3.41 | orange-red brown; Biaxial (-); refract index: n$_α$ = 1.723 n$_β$ = 1.744 n$_γ$ = 1.750 Birefringence: 0.027 |
| Kraisslite | Zn$_3$(Mn,Mg)$_{25}$(Fe$^{3+}$,Al)(As$^{3+}$O$_3$)$_2$[(Si,As$^{5+}$)O$_4$]$_{10}$(OH)$_{16}$ | 5:1 | Orthorhombic | C222$_1$ | a = 8.1821 b = 14.1946 c = 43.9103 Z=4 | 5099.8 | 3.876 | pale red; Uniaxial (+) Refractive index: n$_ε$ = 1.805 |
| Mcgovernite | Mn$_{19}$Zn$_3$(AsO$_4$)$_3$(AsO$_3$)(SiO$_4$)$_3$(OH)$_{21}$ | 3:1 | trigonal | R3m or R3m | a = 8.22 c = 203.1 Z=6 | 11,887.52 | 3.719 | brown; Uniaxial (+) Refractive index: n$_ω$ = 1.757 n$_ε$ = 1.760 Birefringence: δ = 0.003 |
| Halilsarpite | [Mg(H$_2$O)$_6$][CaAs$^{3+}$$_2$(Fe$^{3+}$$_{2.67}$Mo$^{6+}$$_{0.33}$)(AsO$_4$)$_2$O$_7$] | | orthorhomnic | Imma | a = 26.489 b = 7.4205 c = 10.4378 | 2051.7 | | lemon yellow; Biaxial (-) refractive index: n$_α$ = 1.646 n$_β$ = 1.765(5) n$_γ$ = 1.815(5) 2V: 62° Max Birefringence: δ = 0.169 |
| Wiklundite | Pb$_2$(Mn$^{2+}$,Zn)$_3$(Fe$^{3+}$,Mn$^{2+}$)$_2$(Mn$^{2+}$,Mg)$_{19}$(As$^{3+}$O$_3$)$_2$[(Si,As$^{5+}$)O$_4$]$_6$(OH)$_{18}$Cl$_6$ | | hexagonal | ? R3c | a = 8.257 c = 126.59 Z = 6 | 7474 | 4.072 | dark reddish brown |
| | Bi$_8$O$_6$(AsO$_3$)$_2$(AsO$_4$)$_2$ | | monoclinic | I2/a | a=24.372 b=5.528 c=29.90 β=99.058 Z=8 | 3978 | 7.652 | colourless |
| | Th(As$^{III}$$_4$As$^V$$_4$O$_{18}$) | 1:1 | monoclinic | C2/c | a=18.2148 b 5.19792 c=17.3588 β=99.1298 Z=4 | 1622.70 | 4.582 | colourless |