Rockbridgeite
Current inventory:  0 gems
 

  
Rockbridgeite is named after the type locality at the Midvale Mine, South Mountain, Midvale, Rockbridge County, Virginia, USA.

Discovered in 1949; IMA status: Valid (pre-IMA; Grandfathered)

Chemistry

Chemical Formula:

(Fe²⁺,Mn²⁺)Fe³⁺₄(PO₄)₃(OH)₅

Iron Manganese Phosphate Hydroxide

Molecular Weight:

648.96 gm

Composition:

Manganese

2.12 %

Mn

2.73 %

MnO

Iron

40.88 %

Fe

8.30 %

FeO / 49.21 % Fe₂O₃

Phosphorus

14.32 %

P

32.81 %

P₂O₅

Hydrogen

0.78 %

H

6.94 %

H₂O

Oxygen

41.91 %

O

100.00 %

100.00 %

= TOTAL OXIDE

Classification

Mineral Classification:

Phosphates

Strunz 8th Ed. ID:

7/B.10-10

Nickel-Strunz 10th Ed. ID:

8.BC.10

8 : PHOSPHATES, ARSENATES, VANADATES
B : Phosphates, etc., with additional anions, without H₂O
C : With only medium-sized cations, (OH, etc.):RO₄ > 1:1 and < 2:1

Related to:

Rockbridgeite Group. Frondelite-Rockbridgeite Series. The Fe²⁺ analogue of Frondelite and Plimerite.

Members of Group:

Rockbridgeite Group: Frondelite, Plimerite, Rockbridgeite

Varieties:

None

Synonyms:

Kobokobite, Mangan-rockbridgeite

Crystal Data

Crystallography:

Orthorhombic - Dipyramidal

Crystal Habit:

Euhedral crystals rare; typically fibrous, elongated along [001], compact radiating, to 3 cm, in crusts, botryoidal and drusy masses.

Twinning:

None

Physical Properties

Cleavage:

Excellent on {100}, Good on {010}, Fair on {001}

Fracture:

Irregular/Uneven

Tenacity:

Brittle

Moh's Hardness:

3.5 - 4.5

Density:

3.45 (g/cm³)

Luminescence:

Not Fluorescent

Radioactivity:

Not Radioactive

Other:

Soluble in HCl, but not in HNO3 or H2SO4

Optical Properties

Color:

Dark green, olive-green, greenish black, black, commonly color-banded; may be bronze-brown, reddish brown when oxidized.

Transparency:

Transparent to Translucent, Opaque

Luster:

Vitreous to Dull

Refractive Index:

1.875 - 1.897  Biaxial ( + ) 

Birefringence:

0.0220

Dispersion:

Strong; r < v, rarely r > v

Pleochroism:

Visible; X = pale brown to pale yellow-brown; Y = bluish green; Z = dark bluish green

Occurances

Geological Setting:

In “Limonite” iron ore deposits; an alteration product of primary phosphates in complex granite pegmatites.

Common Associations:

Triphylite, Huréaulite, Barbosalite, Roscherite, “Limonite”

Common Impurities:

None

Type Locality:

Midvale Mine, South Mountain, Midvale, Rockbridge County, Virginia, USA

Year Discovered:

1949

View mineral photos:

Rockbridgeite Mineral Photos and Locations

More Information

Mindat.org
Webmineral.com

Rockbridgeite is named after the type locality at the Midvale Mine, South Mountain, Midvale, Rockbridge County, Virginia, USA. It is a common mineral but rarely available as a faceted gem. It's not that it couldn't be faceted but that it is mostly unremarkable as a gem. It usually has a dark green color but that changes with oxidation to a reddish brown, dark brown or black. Rockbridgeite is a ferrous iron rich mineral but its chemistry is a bit odd in that it includes two different iron atoms. One is ferric (with a plus 3 charge) and the other is ferrous (with a plus 2 charge). Rockbridgeite forms from the alteration (oxidation) of primary iron and manganese phosphates.

Distribution: Widespread; may be locally abundant. In the USA, in Virginia, on South Mountain, southeast of Midvale, Rockbridge County; at the Palermo #1 and Fletcher mines, North Groton, Grafton County, New Hampshire; in the Tip Top, Bull Moose, and other mines, near Custer, Custer County, and at the Big Chief, Etta, and other mines, near Keystone, Pennington County, South Dakota. From the Énio pegmatite mine, northeast of Galiléia, and near São Jose da Safira, Agua Boa, Minas Gerais, Brazil. From the El Criollo pegmatite, Cerro Blanco, Tanti district, 45 km west of Córdoba, Córdoba Province, Argentina. At Sabugal, Mangualde, Bendada, and Moreira, Portugal. From the La Vilate quarry, near Chanteloube, Haute-Vienne, France. In Germany, at Hagendorf, and on the Kreuzberg, Pleystein, Bavaria; and from Ullersreuth, Saxony. In the Moculta phosphate quarry, northeast of Angaston, South Australia. From the Sandamap pegmatite, west of Usakos, Namibia. In the Pearl mine, Miami, Zimbabwe. At Tazenakht, Morocco.
 

  
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