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Fergusonite-(Ce)
Current inventory:  0 gems
 

Chemistry:  (Ce,La,Y)NbO₄

Discovered in 1827;   IMA status: Valid (pre-IMA; Grandfathered).
Fergusonite-(Ce) is named in honor of Robert Ferguson (1767–1840), landowner, politician, and mineral collector, of Raith, near Kirkaldy, Scotland, and for its predominant cerium content.

Classification

Mineral Classification:

Sulfates

Strunz 8th Ed. ID:

4/D.24-50

Nickel-Strunz 10th Ed. ID:

7.GA.05

7 : SULFATES (selenates, tellurates, chromates, molybdates, wolframates)
G : Molybdates, Wolframates and Niobates
A : Without additional anions or H₂O

Related to:

Fergusonite-(Y) - Formanite-(Y) Series. Dimorphous with Fergusonite-beta-(Ce).

Crystal Data

Crystallography:

Tetragonal - Dipyramidal

Crystal Habit:

As prismatic to acicular dipyramidal crystals, to 20 cm; granular, massive.

Twinning:

None

Physical Properties

Cleavage:

[1011] Distinct/Good

Fracture:

Conchoidal

Tenacity:

Brittle

Hardness (Mohs):

5.5 - 6.5

Density:

5.45 - 5.48 (g/cm³)

Luminescence:

None

Radioactivity:

Weak; GRapi = 40,097.08 (Gamma Ray American Petroleum Institute Units)

Optical Properties

Color:

Brownish Black to Black; if altered: Brown, Yellow or Gray

Transparency:

Semi-Transparent to Opaque

Luster:

Vitreous, Adamantine, Sub-Metallic; alters to a Dull surface

Refractive Index:

2.20 - 2.30  Uniaxial ( - ); Isotropic if metamict

Birefringence:

0.100

Dispersion:

n/a

Pleochroism:

Weak

Occurances

Geological Setting:

In a carbonatite (Novopoltavsk massif, Russia); in magnesium-rich skarn of the outer granite contact zone of a carbonatite-derived dolomitic marble (Bayan Obo, China).

Common Associations:

Magnetite, phlogopite, graphite, chlorite, quartz, pyrite, columbite, allanite, bastnäsite, parisite, apatite, uranpyrochlore, aeschynite, fersmite, monazite, calcite, dolomite (Novopoltavsk massif, Russia).

Type Locality:

Chernigovskaya Zone, Novopoltavskii Massif, Azov Sea Region, Zaporozh'e Oblast', Ukraine

Year Discovered:

1827

View mineral photos:

Fergusonite Mineral Photos and Locations

More Information

Mindat.org
Webmineral.com

Fergusonite-(Ce) is a rare sulfate mineral that is very rarely available as faceted gems. Cabochons have been cut as curiosities as they have no special features except rarity. Faceted gems are extremely rare and are cut just as collector's gems. Fergusonite-(Ce) is weakly radioactive due to its cerium (Ce) content.

The only source of gemmy crystals large enough for faceting is a recent find in Madagascar. These other sources produce only translucent to opaque massive material or transparent crystals that are too small for faceting: Chernigovskaya zone, Novopoltavskii massif, Azov Sea area, Ukraine; eastern Bayan Obo Fe–Nb–RE deposit, 130 km north of Baotou, Inner Mongolia, China; Granite Mountain, near Little Rock, Pulaski Co., Arkansas, USA.
 

  
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