TY - JOUR
T1 - Segerstromite, Ca3(As5+O4)2[As3+(OH)3]2, the first mineral containing As3+(OH)3, the arsenite molecule, from the Cobriza mine in the Atacama Region, Chile
AU - Yang, Hexiong
AU - Downs, Robert T.
AU - Jenkins, Robert A.
AU - Evans, Stanley H.
N1 - Funding Information:
This study was funded by the Science Foundation Arizona. The constructive comments by Anthony R. Kampf and an anonymous reviewer are greatly appreciated.
Publisher Copyright:
© 2018 Walter de Gruyter GmbH, Berlin/Boston.
PY - 2018/9/25
Y1 - 2018/9/25
N2 - A new mineral species, segerstromite, ideally Ca3(As5+O4)2[As3+(OH)3]2, has been discovered at the Cobriza mine in the Sacramento district in the Copiapó Province, Chile. Crystals of segerstromite occur as tetrahedra, dodecahedra (up to 0.50 × 0.50 × 0.50 mm), or in blocky aggregates. Associated minerals include talmessite, vladimirite, and Sr-bearing hydroxylapatite. Similar to the associated minerals, segerstromite is a secondary mineral. The new mineral is colorless in transmitted light, transparent with a white streak and vitreous luster. It is brittle and has a Mohs hardness of ∼4.5. No cleavage, parting, or twinning was observed. The measured and calculated densities are 3.44(3) and 3.46 g/cm3, respectively. Optically, segerstromite is isotropic, with n = 1.731(5). It is insoluble in water or hydrochloric acid. An electron microprobe analysis yielded an empirical formula (based on 14 O apfu) Ca2.98(AsO4)2.00[As(OH)3]2.00. Segerstromite is cubic, with space group I213 and unit-cell parameters a = 10.7627(2) Å, V = 1246.71(4) Å3, and Z = 4. Its crystal structure is constructed from three different polyhedral units: distorted CaO8 cubes, rigid As5+O4 arsenate tetrahedra, and neutral As3+(OH)3 arsenite triangular pyramids. The Ca-groups form layers of corrugated crankshaft chains that lie parallel to the cubic axes. These chains are linked by the isolated As5+O4 and As3+(OH)3 groups. Segerstromite is the first known crystalline compound that contains the As3+(OH)3 arsenite molecule, pointing to a new potential approach to remove highly toxic and mobile As3+(OH)3 from drinking water.
AB - A new mineral species, segerstromite, ideally Ca3(As5+O4)2[As3+(OH)3]2, has been discovered at the Cobriza mine in the Sacramento district in the Copiapó Province, Chile. Crystals of segerstromite occur as tetrahedra, dodecahedra (up to 0.50 × 0.50 × 0.50 mm), or in blocky aggregates. Associated minerals include talmessite, vladimirite, and Sr-bearing hydroxylapatite. Similar to the associated minerals, segerstromite is a secondary mineral. The new mineral is colorless in transmitted light, transparent with a white streak and vitreous luster. It is brittle and has a Mohs hardness of ∼4.5. No cleavage, parting, or twinning was observed. The measured and calculated densities are 3.44(3) and 3.46 g/cm3, respectively. Optically, segerstromite is isotropic, with n = 1.731(5). It is insoluble in water or hydrochloric acid. An electron microprobe analysis yielded an empirical formula (based on 14 O apfu) Ca2.98(AsO4)2.00[As(OH)3]2.00. Segerstromite is cubic, with space group I213 and unit-cell parameters a = 10.7627(2) Å, V = 1246.71(4) Å3, and Z = 4. Its crystal structure is constructed from three different polyhedral units: distorted CaO8 cubes, rigid As5+O4 arsenate tetrahedra, and neutral As3+(OH)3 arsenite triangular pyramids. The Ca-groups form layers of corrugated crankshaft chains that lie parallel to the cubic axes. These chains are linked by the isolated As5+O4 and As3+(OH)3 groups. Segerstromite is the first known crystalline compound that contains the As3+(OH)3 arsenite molecule, pointing to a new potential approach to remove highly toxic and mobile As3+(OH)3 from drinking water.
KW - New mineral
KW - Raman spectrum
KW - X-ray diffraction
KW - arsenate/arsenite
KW - crystal structure
KW - segerstromite
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U2 - 10.2138/am-2018-6329
DO - 10.2138/am-2018-6329
M3 - Article
AN - SCOPUS:85053289514
SN - 0003-004X
VL - 103
SP - 1497
EP - 1501
JO - American Mineralogist
JF - American Mineralogist
IS - 9
ER -