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Macfallite  (inclusions in Quartz)
Current inventory:  0 gems
 

  
Macfallite is named for US author and amateur mineralogist Russell Patterson MacFall (1903-1983).

Discovered in 1974;   IMA status: Valid (IMA approved).

Chemistry

Chemical Formula:

Ca₂Mn³⁺_2.5Al_0.5(SiO₄)(Si₂O₇)(OH)₃

Calcium Manganese Aluminum Silicate Hydroxide

Molecular Weight:

542.26 gm

Composition: 

Classification

Mineral Classification:

Silicates (Germanates)

Strunz 8th Ed. ID:

8/C.24-10

Nickel-Strunz 10th Ed. ID:

9.BG.15

9 : SILICATES (Germanates)
B : Sorosilicates
G : Sorosilicates with mixed SiO₄ and Si₂O₇ groups; cations in octahedral [6] and greater coordination

Related to:

Pumpellyite Group.

Synonyms:

IMA1974-057

Crystal Data

Crystallography:

Monoclinic - Prismatic

Crystal Habit:

Rare single crystals, elongated, to 1 cm, invariably twinned; as radial and framboidal aggregates; in fine intergrowths with orientite; massive.

Twinning:

Twinning common; by reflection on [100], commonly repeated.

Physical Properties

Cleavage:

[001] Perfect

Fracture:

Irregular/Uneven, Conchoidal

Tenacity:

Brittle

Moh's Hardness:

5.0 - 5.5

Density:

3.43 (g/cm³)

Luminescence:

None

Radioactivity:

Not Radioactive

Optical Properties

Color:

Brown, Reddish Brown, Maroon, dull Pink

Transparency:

Transparent to Translucent

Luster:

Silky to Subadamantine

Refractive Index:

1.773 - 1.815  Biaxial ( + ) or ( - )

Birefringence:

0.037 - 0.040

Dispersion:

Medium; r < v

Pleochroism:

X = colorless to yellow; Y = light brown; Z = dark brown to reddish brown

Occurances

Geological Setting:

In abundance, replacing Calcite in fissures and in lenses in basalt (Manganese Lake, Michigan, USA); replacing Braunite under low-temperature metamorphic conditions (Faggiona, Italy).

Common Associations:

Braunite, Manganite, Orientite, Pyrolusite (Manganese Lake, Michigan, USA); Braunite, Carbonates, Manganoan Richterite, Quartz (Faggiona, Italy).

Common Impurities:

Ti, Al, Fe, Cr, V, Cu, Mg, K, Na, H₂O

Type Locality:

Manganese Mine, Copper Harbor, Keweenaw Co., Michigan, USA

Year Discovered:

1974

View mineral photos:

Macfallite Mineral Photos and Locations

More Information

Mindat.org
Webmineral.com

Macfallite is a relatively new species discovered in 1974 which occurrs as aggregates and also as reddish brown to maroon inclusions in Quartz. It is also found as brown to dull pink compact massive material.

Macfallite is found near Manganese Lake, Copper Harbor, Keweenaw County, Michigan, USA and in Italy, in the Cerchiara mine, Faggiona, La Spezia, Liguria.
 

  
Macfallite gems for sale:

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