Bruce T. Mitchell's Photo Gallery

0JG-H4CMagnesite MgCO₃ , Deweylite Mg₄Si₃O₁₀·6H₂O ?

Goat Hill Magnesia Quarries, West Nottingham Township, Chester County, Pennsylvania, USA

Dimensions: 5.5 cm x 3 cm x 2 cm

Specimen of massive magnesite, with a coating of tan deweylite, taken under ordinary light

448-VY1Magnesite MgCO₃ , Serpentine Subgroup D₃[Si₂O₅](OH)₄

Goat Hill Magnesia Quarries, West Nottingham Township, Chester County, Pennsylvania, USA

Dimensions: 8 cm x 5 cm x 5 cm

Veins of white magnesite (5-8mm) running through massive serpentinite rock, a rock composed primarily of serpentine, with some chlorite

Q59-7K3Magnesite MgCO₃ , Serpentine Subgroup D₃[Si₂O₅](OH)₄

Goat Hill Magnesia Quarries, West Nottingham Township, Chester County, Pennsylvania, USA

Dimensions: 7 cm x 3 cm x 2.5 cm

Massive magnesite, with some included green serpentine, from the E. wall of the Goat Hill Magnesia Quarry, within the boundary of the Goat Hill Serpentine Barrens.

HN4-T6JIlmenite Fe²⁺TiO₃ , Quartz SiO₂

Wissahickon Valley, Philadelphia, Philadelphia County, Pennsylvania, USA

Dimensions: 6.5 cm x 4 cm x 3 cm

Bright, metallic ilmenite** coating gray quartz, from the Wissahickon Valley area. This is a part of the Wissahickon Formation. (** possibly hematite, not ilmenite although less likely in this case)

NHN-34CTourmaline AD₃G₆ (T₆O₁₈)(BO₃)₃X₃Z , Muscovite KAl₂(AlSi₃O₁₀)(OH)₂

Wissahickon Valley, Philadelphia, Philadelphia County, Pennsylvania, USA

Dimensions: 12.5 cm x 12 cm x 3 cm
Largest Crystal Size: 2.5 cm

Schorl (black tourmaline) is one of the more interesting minerals that can be found in the Wissahickon Valley mica schists. Usually the crystals are fairly small but here, the black schorl crystals are 1.5-2.5 cm long.

THQ-VM7Fluorapatite Ca₅(PO₄)₃F , Andradite Ca₃Fe³⁺₂(SiO₄)₃ , Calcite CaCO₃

Buckwheat dump mineral collecting site, Franklin Mine, Franklin, Sussex County, New Jersey, USA

Dimensions: 7 cm x 5.5 cm x 5 cm

This is one of the best pieces of fluorapatite that I've found at Franklin, with a bright "peach" or pinkish-orange fluorescence under shortwave UV, comparable in intensity to calcite. The Picking Table (Vol 57, No.2, Fall, 2016) describes this type as being REE -rich, as well as containing considerable arsenic, although the fluorescence itself is probably due to Mn and REE elements. For this reason, such specimens were originally classified as svabite by early collectors. There is minor calcite (fl orange red) associated with it.

K91-NTCStaurolite Fe²⁺₂Al₉Si₄O₂₃(OH)

Wissahickon Valley, Philadelphia, Philadelphia County, Pennsylvania, USA

Dimensions: 7 cm x 6 cm x 3 cm
Largest Crystal Size: 4 cm

A single, large and well-formed crystal of dark brown staurolite in a matrix of muscovite (mica) schist.

18A-HWRStaurolite Fe²⁺₂Al₉Si₄O₂₃(OH) , Muscovite KAl₂(AlSi₃O₁₀)(OH)₂ , Quartz SiO₂

Wissahickon Valley, Philadelphia, Philadelphia County, Pennsylvania, USA

Dimensions: 6 cm x 5 cm x 3.5 cm
Largest Crystal Size: 2.5 cm

This is a single crystal of dark brown staurolite embedded in a matrix of mica schist (muscovite mica and gray quartz). The crystal has been naturallly fractured at one place from the tectonic stresses, so it looks slightly bent.

E7M-DT6Anthophyllite ◻{Mg₂}{Mg₅}(Si₈O₂₂)(OH)₂ , Talc Mg₃Si₄O₁₀(OH)₂

Wissahickon Valley, Philadelphia, Philadelphia County, Pennsylvania, USA

Dimensions: 7 cm x 6 cm x 2.5 cm

This specimen features anthophyllite, observable as the fibrous, mocha-colored mineral, occurring in weathered cavities in a talc-rich schist. The silvery-colored schist is soft, and slippery, and likely would accurately be described as a soapstone.

UGQ-MG0Magnetite Fe²⁺Fe³⁺₂O₄ , Chlorite Group

Wissahickon Valley, Philadelphia, Philadelphia County, Pennsylvania, USA

Dimensions: 10.5 cm x 7 cm x 2 cm

From the Wissahickon Valley in Philadelphia, this specimen has several very sharp magnetite octahedrons embedded in a chlorite schist. The larger crystals measure about 5-6 mm on an edge.