| Seamanite | |
| Category: | Borate minerals |
| Boxwidth: | 280px |
| Formula: | Mn3[B(OH)<sub>4</sub>](PO4)(OH)2 |
| Imasymbol: | Sem[1] |
| Molweight: | 372.64 g/mol[2] |
| Strunz: | 6.AC.65 |
| Dana: | 43.4.5.1 |
| System: | Orthorhombic |
| Class: | Dipyramidal (mmm) H-M symbol: (2/m 2/m 2/m) |
| Symmetry: | Pbnm |
| Unit Cell: | a = 7.811 Å, b = 15.114 Å c = 6.691 Å, Z = 4 |
| Color: | yellow, yellow-brown, pink[3] |
| Habit: | acicular |
| Cleavage: | distinct on |
| Fracture: | brittle |
| Tenacity: | brittle |
| Mohs: | 4 |
| Luster: | vitreous |
| Refractive: | nα = 1.640, nβ = 1.663, nγ = 1.665 |
| Birefringence: | δ = 0.025 |
| 2V: | ≈40°[4] |
| Dispersion: | weak |
| Fluorescence: | none |
| Streak: | white |
| Gravity: | 3.08 |
| Density: | 3.08–3.128 g/cm3 |
| Solubility: | in cold, dilute acids |
| Diaphaneity: | transparent |
| References: | [5] |
Seamanite, named for discoverer Arthur E. Seaman, is a rare manganese boron phosphate mineral with formula Mn3[B(OH)<sub>4</sub>](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., seamanite is known from four sites in Michigan and South Australia.
In 1917, Arthur E. Seaman collected a mineral sample from the Chicagon Mine in Iron County, Michigan. 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)<sub>4</sub>](PO4)(OH)2.[8]
Seamanite is a transparent, yellow to pink mineral that occurs as needle-shaped crystals.[2] Seamanite is a brittle mineral with a mohs hardness of 4.[3] 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]
, 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.[3]
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.[5]
Seamanite is formed of acicular crystals elongated along [001] and showing the faces and 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.[5]