MacFallite (inclusions in Quartz)
Current inventory: 0 gems
 

  
MacFallite was named by Paul Moore et al. to honor author and amateur mineralogist Russell "Russ" Patterson MacFall (1903-1983) from Illinois, USA.

Discovered in 1974; IMA status: Valid (IMA Approved 1974)

Chemistry

Chemical Formula:

Ca₂Mn₃³⁺(SiO₄)(Si₂O₇)(OH)₃

Calcium Manganese Silicate Hydroxide

Molecular Weight:

544.17 gm

Composition:

Sodium

0.04 %

Na

0.06 %

Na₂O

Calcium

14.95 %

Ca

20.92 %

CaO

Magnesium

0.40 %

Mg

0.67 %

MgO

Manganese

25.34 %

Mn

36.41 %

Mn₂O₃

Aluminum

1.34 %

Al

2.53 %

Al₂O₃

Vanadium

0.09 %

V

0.14 %

V₂O₃

Copper

0.35 %

Cu

0.44 %

CuO

Silicon

15.74 %

Si

33.68 %

SiO₂

Hydrogen

0.58 %

H

5.16 %

H₂O

Oxygen

41.16 %

O

100.00 %

100.00 %

= TOTAL OXIDE

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:

None

Varieties:

None

Synonyms:

ICSD 1612, IMA1974-057, PDF 42-601

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:

By reflection on {100}, commonly repeated. 

Physical Properties

Cleavage:

Perfect on {001}

Fracture:

Irregular/Uneven Conchoidal Fibrous Hackly Micaceous None observed Splintery Step-like Sub-Conchoidal

Tenacity:

Brittle

Moh's Hardness:

5.0 - 5.5

Density:

3.43 (g/cm³)

Luminescence:

None

Radioactivity:

Not Radioactive

Optical Properties

Color:

Reddish brown, maroon, dull pink

Transparency:

Transparent to translucent

Luster:

Silky to sub-adamantine

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:

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

Common Impurities:

Ti, Al, Fe, Cr, V, Cu, Mg, K, Na, H₂O

Type Locality:

Manganese Mine, Copper Harbor, Keweenaw County, Michigan, USA

Year Discovered:

1974 (IMA Approved 1974)

View mineral photos:

MacFallite Mineral Photos and Locations

Unusual Gem Categories

Inclusions in Quartz

More Information

Mindat.org
Webmineral.com

MacFallite is a relatively new mineral species discovered in 1974 at the Manganese Mine, Copper Harbor, Keweenaw County, Michigan, USA. MacFallite occurrs as radial aggregates of reddish-brown, or maroon to dull pink compact massive material. It is also found as tiny, reddish brown radial crystal inclusions in Quartz along with inclusions of orange skeletal crystals of Johnsenite-(Ce) (incl.) and black Braunite crystals from the Arthur Costa mine, Jaguaracu, Minas Gerais, Brazil. The picture above shows a faceted Quartz gem with inclusions of a reddish brown radiating crystal of MacFallite along with an orange skeletal crystal of Johnsenite-(Ce). If you place your cursor over the picture you will see a magnified picture of the MacFallite crystal.

MacFallite was named by Paul Moore et al. to honor author and amateur mineralogist Russell Patterson MacFall (1903-1983) from Illinois, USA. Russell "Russ" MacFall, was a consummate newspaper man and the author of several books and hundreds of magazine articles on mineral collecting. Among his books were Gem Hunter's Guide (1951, 1958, 1963, 1969), Fossils for Amateurs (1972, 1983), Popular Mechanics Complete Book of Rocks, Minerals, Gems, Fossils (1978), Rock Hunter's Guide (1980), Collecting Rocks, Minerals, Gems and Fossils (1963, 1964, 1966, 1968), Minerals and Gems (1975) and The Complete Book of Rocks, Minerals, Gems, Fossils (1978), not to mention a biography of L. Frank Baum (author of the Wizard of Oz stories). He served as President of the Midwest Federation of Mineralogical and Geological Societies. During his last years he also served as honorary curator of minerals at the San Diego Museum of Natural History.

Macfallite distribution: found at the Manganese Mine, Copper Harbor, Keweenaw County, Michigan, USA. In Italy, in the Cerchiara mine, Faggiona, La Spezia, Liguria. As inclusions in Quartz from the Arthur Costa mine, Jaguaracu, Minas Gerais, Brazil.
 

  
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