Seamanite
Rare manganese boron phosphate mineral
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Seamanite, named for discoverer Arthur E. Seaman, is a rare manganese boron phosphate mineral with formula Mn3[B(OH)4](PO4)(OH)2. The yellow to pink mineral occurs as small, needle-shaped crystals. It was first discovered in 1917 from a mine in Iron County, Michigan, United States and identified in 1930. As of 2012[update], seamanite is known from four sites in Michigan and South Australia.
| Seamanite | |
|---|---|
Seamanite crystals on a rock sample (5 x 4 x 3 cm) | |
| General | |
| Category | Borate minerals |
| Formula | Mn3[B(OH)4](PO4)(OH)2[1] |
| IMA symbol | Sem[2] |
| Strunz classification | 6.AC.65[3] |
| Dana classification | 43.4.5.1[1] |
| Crystal system | Orthorhombic |
| Crystal class | Dipyramidal (mmm) H-M symbol: (2/m 2/m 2/m)[4] |
| Space group | Pbnm |
| Unit cell | a = 7.811 Å, b = 15.114 Å c = 6.691 Å, Z = 4 |
| Identification | |
| Formula mass | 372.64 g/mol[3] |
| Color | yellow, yellow-brown, pink[1] |
| Crystal habit | acicular[3] |
| Cleavage | distinct on {001}[4] |
| Fracture | brittle[3] |
| Tenacity | brittle[4] |
| Mohs scale hardness | 4[1] |
| Luster | vitreous[3] |
| Streak | white[3] |
| Diaphaneity | transparent[4] |
| Specific gravity | 3.08[1] |
| Density | 3.08–3.128 g/cm3[4] |
| Refractive index | nα = 1.640, nβ = 1.663, nγ = 1.665[5] |
| Birefringence | δ = 0.025[1] |
| 2V angle | ≈40°[5] |
| Dispersion | weak[1] |
| Ultraviolet fluorescence | none[3] |
| Solubility | in cold, dilute acids[1] |
| References | [4] |
History
In 1917, Arthur E. Seaman collected a mineral sample from the Chicagon Mine in Iron County, Michigan.[a] He correctly believed it to be a new mineral species based on a qualitative analysis of its composition by F. B. Wilson. World War I delayed further study of the mineral until 1929. A study in 1930 proved it to be a new mineral and named it seamanite in honor of Seaman. They cited his career as a professor of geology and mineralogy and his contributions to the field as reasons for the naming.[6]
The original analysis of the mineral in 1930 suggested seamanite to be a hydrated salt.[7] However, in 1971, the mineral was determined to be the coordination compound Mn3[B(OH)4](PO4)(OH)2.[8]
Description
Seamanite is a transparent, yellow to pink mineral that occurs as needle-shaped crystals.[3] Seamanite is a brittle mineral with a mohs hardness of 4.[1] It is found in the crevices of fractured siliceous rock.[6] The type occurrence was found in association with small crystals of calcite, thin coatings of manganese oxide,[6] and fibrous sussexite.[9] Seamanite has also been found with shigaite.[10]
Distribution
As of 2012[update], seamanite is known from four locations: the Cambria-Jackson Mine in Marquette County, Michigan, the Chicagon Mine and the Bengal Mine in Iron County, Michigan, and the Iron Monarch open cut in the Eyre Peninsula, South Australia.[1]
The type material is stored at Michigan Technological University in Houghton, Michigan, and at the National Museum of Natural History in Washington, D.C. as sample 96282.[4]
Crystallography
gray:H red:O green:B violet:Mn center of yellow tetrahedrons:P
Seamanite is formed of acicular crystals elongated along [001] and showing the faces {110} and {111} up to one centimeter. It has an orthorhombic crystal system and the Pbnm space group. The parameters of its unit cell are: a=7.811 Å, b=15.114 Å, c=6.691 Å, Z=4 units per unit cell.[4]
