Seamanite

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

Crystal structure of seamanite:
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]

Notes

1. Some sources list it as the Chicagoan Mine^[3]