Seamanite

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Seamanite
Seamanite-zr17a.jpg
Seamanite crystals on a rock sample
(5 x 4 x 3 cm)
General
Category Borate minerals
Formula
(repeating unit)
Mn3[B(OH)4](PO4)(OH)2[1]
Strunz classification 06.AC.65[2]
Dana classification 43.4.5.1[1]
Unit cell a=7.811 Å, b=15.114 Å, c=6.691 Å, Z=4
Identification
Formula mass 372.64 g/mol[2]
Color yellow, yellow-brown, pink[1]
Crystal habit acicular[2]
Crystal system orthorhombic[3]
Cleavage distinct on {001}[3]
Fracture brittle[2]
Tenacity brittle[3]
Mohs scale hardness 4[1]
Luster vitreous[2]
Streak white[2]
Diaphaneity transparent[3]
Density 3.08–3.128 g/cm3[3]
Refractive index nα = 1.640,
nβ = 1.663,
nγ = 1.665[4]
Birefringence δ = 0.025[1]
2V angle ≈40°[4]
Dispersion weak[1]
Ultraviolet fluorescence none[2]
Solubility in cold, dilute acids[1]

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, seamanite is known from four sites in Michigan and South Australia.

History[edit]

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.[5]

The original analysis of the mineral in 1930 suggested seamanite to be a hydrated salt.[6] However, in 1971, the mineral was determined to be the coordination compound Mn3[B(OH)4](PO4)(OH)2.[7]

Description[edit]

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.[1] It is found in the crevices of fractured siliceous rock.[5] The type occurrence was found in association with small crystals of calcite, thin coatings of manganese oxide,[5] and fibrous sussexite.[8] Seamanite has also been found with shigaite.[9]

Distribution[edit]

As of 2012, 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.[3]

Crystallography[edit]

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.[3]

Notes[edit]

  1. ^ Some sources list it as the Chicagoan Mine[2]

References[edit]

  1. ^ a b c d e f g h i "Seamanite". Mindat. Retrieved April 13, 2012. 
  2. ^ a b c d e f g h i "Seamanite Mineral Data". Webmineral. Retrieved April 13, 2012. 
  3. ^ a b c d e f g "Seamanite" (PDF). Handbook of Mineralogy. Mineral Data Publishing. Retrieved April 13, 2012. 
  4. ^ a b Kraus, p. 222
  5. ^ a b c Kraus, p. 220.
  6. ^ Kraus, p. 223–5
  7. ^ Moore, p. 1527.
  8. ^ Slawson, p. 575
  9. ^ "Seamanite - Photo Gallery". Mindat. Retrieved April 13, 2012. 

Bibliography[edit]

Further reading[edit]

External links[edit]

Media related to Seamanite at Wikimedia Commons