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Phosphate Rare Minerals for the Collector

Friday, 26 August 2016 12:00 PM

Primary and Metasomatic phosphates are found mostly in pegmatites, but also occur in many sedimentary deposits. Most of these phosphates look the same. We will attempt to unlock the mystery of these unique minerals which can often contain secondary phosphate minerals. 

Ferrowyllieite

#41619
Locality
Victory mine, Custer Co., South Dakota, United States 
Formula
Na2Fe2+2Al(PO4)3 
Availability
Sold
Size
4.5 x 3 x 3 cm - Miniature 
Tagged
phosphate , pegmatite mineral  
Special Info
Type Locality 

Black mass of crystalline Ferrowyllieite. The mine is now Custer's sewage lagoon. Originally found at this mine with Arrojadite. Crystals occur up to 10cm. When published it was named Wyllieite and later renamed to Ferrowyllieite.


Ferrowyllieite

Formula
Na2Fe2+2Al(PO4)3 
Crystal System
Monoclinic 
Crystal Habit
Euhedral Crystals, Selvage 
Cleavage
Perfect, Distinct, None 
Luster
Vitreous - Metallic 
Color
bluish green, greenish black, gray green, dark blue green 
Streak
gray green 
Class
Monoclinic - Prismatic 
Fracture
Brittle 
Hardness
Special Info
Type Locality
SOLD
Fillowite - 45211
Fillowite - 45211

Fillowite

#45211
Locality
Kiluli, Western prov., Rwanda 
Formula
Na2CaMn2+7(PO4)6 
Availability
Sold
Size
3 x 3.5 x 1.5 cm - Miniature 
Tagged
phosphate , pegmatite mineral  

Glassy dark green partly yellowish green crystalline mass. Originally found in the Fillow lithium pegmatite of Branchville, CT and published by Brush and Dana in 1879. It is rare having been found in less than 15 occurences worldwide. The original description makes reference to an unknown substance which may be an oxidation product on the Fillowite from Branchville. This specimen also has a white caking on the outer edge of the weathered side of the Fillowite. Perhaps this is the same sort of white material reported by Dana. It appears that the Fillowite oxidizes and perhaps lead to secondaries. It is associated with probably Sicklerite and purple Heterosite.


Fillowite

Formula
Na2CaMn2+7(PO4)6 
Crystal System
Trigonal 
Crystal Habit
Granular, Euhedral Crystals 
Cleavage
Perfect, None, None 
Luster
Resinous - Greasy 
Color
yellow, reddish brown, colorless 
Streak
white 
Class
Trigonal - Rhombohedral 
Fracture
Brittle - Uneven 
Hardness
4.5 

Frondelite

#41603
Locality
Tip Top mine, Custer Co., South Dakota, United States 
Formula
Mn2+Fe3+4(PO4)3(OH)5 
Availability
Sold
Size
6.5 x 4.5 x 4 cm - Sm Cabinet 
Tagged
phosphate , pegmatite mineral  

Frondelite is the Mn analogue of Rockbridgeite. My only basis for calling this "Frondelite" is that it is brown. Rockbridgeite is usually black and Frondelite is usually brown. And of course there's always exceptions and Rockbridgeite has shades of green and Frondelite can be black. Someday I'll sit down with my pocket EDS and analyze all the zones of chemical variations.  

The best Rockbridgeite is acicular free-standing radial groups in altered Triphylite vugs. Rockbridgeite also occurs as embedded hairlike masses just like this specimen but black. This piece is mainly altered primary Triphylite maybe a metasomatic product, which is my reasoning for placing it in this gallery. 


Frondelite

Formula
Mn2+Fe3+4(PO4)3(OH)5 
Crystal System
Orthorhombic 
Cleavage
Perfect, Distinct, Distinct 
Luster
Vitreous - Dull 
Color
brown, brown green, brownish black, green black, dark green 
Streak
brownish gray 
Class
Orthorhombic - Dipyramidal 
Fracture
Brittle - Uneven 
Hardness
4.5 

Graftonite

#PD41610
Locality
Bull Moose mine, Custer Co., South Dakota, United States 
Formula
(Fe2+,Mn2+,Ca)3(PO4)2 
Availability
Sold
Size
4.5 x 4 x 3 cm - Miniature 
Tagged
phosphate , pegmatite mineral  

Reddish brown lamellae of Graftonite with Triphylite. 


Graftonite

Formula
(Fe2+,Mn2+,Ca)3(PO4)2 
Crystal System
Monoclinic 
Crystal Habit
Massive - Granular, Lamellar 
Cleavage
Perfect, None, None 
Luster
Vitreous - Greasy 
Color
brown, pink, dark brown, reddish brown 
Streak
pale pink 
Class
Monoclinic - Prismatic 
Fracture
Uneven 
Hardness
Collection
Phillips Collection

Graftonite

with Sarcopside - #43827
Locality
Berg, Sollefteå, Ångermanland, Sweden 
Formula
(Fe2+,Mn2+,Ca)3(PO4)2 
Availability
Sold
Size
3 x 2 x 1.5 cm - Thumbnail 
Tagged
phosphate , pegmatite mineral  

Brownish red mass with laminations of Sarcopside. The two minerals are related but not as a series. Both contain ferrous iron (Fe+2). Very few if any primary phosphates crystallize with ferric iron (Fe+3), since most of the rock forming minerals such as schorl and biotite will hog it all. Rosemaryite (see this Special Edition update) is an exception. According to Moore (Min. Rec. 1973), Graftonite usually forms with Sarcopside as alternating lamellae, unless much lithium is present in the parent melt upon which Triphyllite will form and alternate with Graftonite (Palermo, Bull Moose). You will see this example with other specimens in this Special Edition.

This locality is a pegmatite in which Graftonite occurs as primary nodules. Graftonite is fairly common in complex, fractionated pegmatites and a brief survey of Mindat localities show this except for one occurence in a meteorite.

Graftonite is fairly resistant to weathering and thus does not usually form secondary phosphate minerals.


Graftonite

Formula
(Fe2+,Mn2+,Ca)3(PO4)2 
Crystal System
Monoclinic 
Crystal Habit
Massive - Granular, Lamellar 
Cleavage
Perfect, None, None 
Luster
Vitreous - Greasy 
Color
brown, pink, dark brown, reddish brown 
Streak
pale pink 
Class
Monoclinic - Prismatic 
Fracture
Uneven 
Hardness

Graftonite

#DS45155
Locality
Palermo mine, Groton, Grafton Co., New Hampshire, United States 
Formula
(Fe2+,Mn2+,Ca)3(PO4)2 
Availability
Sold
Size
7.5 x 5.5 x 3 cm - Sm Cabinet 
Tagged
phosphate , pegmatite mineral  

A large cleaved mass of reddish brown Graftonite showing typical lamellae in cross-section. See Graftonite 43827 for a review on this mineral.


Graftonite

Formula
(Fe2+,Mn2+,Ca)3(PO4)2 
Crystal System
Monoclinic 
Crystal Habit
Massive - Granular, Lamellar 
Cleavage
Perfect, None, None 
Luster
Vitreous - Greasy 
Color
brown, pink, dark brown, reddish brown 
Streak
pale pink 
Class
Monoclinic - Prismatic 
Fracture
Uneven 
Hardness
Collection
Shultz Collection

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