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Pegmatites

Monday, 28 January 2013 08:00 AM

Since we live in the Black Hills, we enjoy our time visiting some of the old pegmatite mines in the Black Hills. But there are pegmatites of all ages, sizes, and shapes all over the world. They also contain some of the largest crystals in the world. Some are famous for their gem quality minerals and some are famous for their minute rare minerals. Join us for a neat review of pegmatite habits, features and of course minerals.

SOLD

Albite

var. cleavelandite - #PD34923

$40.00 - Sold
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Locality: Himalaya mine, San Diego Co., California, United States
Formula: NaAlSi₃O₈
Availability: Sold
Size: 7 x 4.5 x 4 cm - Sm Cabinet
Tagged: pegmatite

Cleavelandite is a variety Albite, the sodic (Na) rich end member of the Albite-Anorthite Series. It is a common variety in most pegmatites and is usually found in white to slightly bluish compact platy masses. In the pegmatites of San Diego county, California, cleaveland forms large cauliflower-like groups with platy crystals in open pockets. This specimen is an excellent example of this habit. As a bonus a small 1.5cm doubly terminated Quartz group occurs on the Albite as well as a small 2mm light purple Fluorapatite crystal.

Albite

Formula: NaAlSi₃O₈
Crystal System: Triclinic
Crystal Habit: Blocky, Striated, Granular
Cleavage: Perfect, Good, None
Luster: Vitreous (Glassy)
Color: white, gray, greenish gray, bluish green, gray
Streak: white
Class: Triclinic - Pinacoidal
Fracture: Uneven
Hardness: 7

Collection: Phillips Collection

On Dakota Matrix: Previously Sold Albite
On Dakota Matrix: Other Available Albite
WebMineral: View Albite
Mindat: View Albite

SOLD

Amblygonite

- Montebrasite - #PD34926

$75.00 - Sold
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Locality: Dunton Gem quarry, Newry, Oxford Co., Maine, United States
Formula: LiAlPO₄F
Availability: Sold
Size: 12 x 8 x 6 cm - Cabinet
Tagged: phosphate , pegmatite

This is an excellent well-formed crystal of the primary phosphate, labeled as "amblygonite." All amblygonites should be labeled as within the series of amblygonite-montebrasite. Montebrasite is the OH analogue whereas amblygonite is the F end member. Ii is doubtful that in hand specimen the two can be discerned. Moore (MR May/June 1973) states that triphylite will crystallize before amblygonite-montebrasite. Crystals are known to be very large up to a meter across in several cases. Perfect crystals are usually not the case since they are typically found as rounded nodules probably a result of metasomatic reactions with the remaining fluid in the pegmatite system so this specimen is a nice example. The outer portion of the specimen is probably altered to kaolinite. Amblygonite can sometimes be hard to tell apart from ordinary feldspars but a simple hardness test can differentiate the two. However, be careful since sometimes amblygonite will have the kaolinite rim.

Amblygonite

Formula: LiAlPO₄F
Crystal System: Triclinic
Crystal Habit: Columnar, Euhedral Crystals, Prismatic
Cleavage: Perfect, Good, Distinct
Luster: Vitreous - Pearly
Color: white, yellow, gray, bluish gray, greenish gray
Streak: white
Class: Triclinic - Pinacoidal
Fracture: Uneven
Hardness: 5.5-6

Collection: Phillips Collection

On Dakota Matrix: Previously Sold Amblygonite
On Dakota Matrix: Other Available Amblygonite
WebMineral: View Amblygonite
Mindat: View Amblygonite

SOLD

Baratovite

in Albite - #PD34934

$175.00 - Sold
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Locality: Darai-Pioz Glacier, Alayskiy Range, Tien Shan Mts, Tajikistan
Formula: KLi₃Ca₇Ti₂(SiO₃)₁₂F₂
Availability: Sold
Size: 11 x 7 x 4 cm - Cabinet
Tagged: pegmatite
Special Info: Fluorescent
Special Info: Type Locality

This occurrence may or may not be classified as a pegmatite, although it certainly pegmatitic - it is igneous and coarse grained. There is more to the definition of a pegmatite, but not here. This specimen is rich in Baratovite, which occurs as coarse cleavable crystal grains to over 1cm. The grains are a bright blue un shortwave UV, However all the pink does not fluoresce, which is puzzling. This is a large specimen with associated sphene and albite.

This locality, according to Mindat, has produced no less than 130 minerals and 30 type locality minerals. The area must be vast as part of the glaciated massif. More on Baratovite can be found in our Mineralpedia.

Baratovite

Formula: KLi₃Ca₇Ti₂(SiO₃)₁₂F₂
Crystal System: Monoclinic
Crystal Habit: Platy, Aggregates
Cleavage: Perfect, None, None
Luster: Vitreous - Pearly
Color: pearl white
Streak: white
Class: Monoclinic - Prismatic
Hardness: 3.5

Collection: Phillips Collection
Special Info: Fluorescent
Special Info: Type Locality

Mineralpedia: View Baratovite
On Dakota Matrix: Previously Sold Baratovite
On Dakota Matrix: Other Available Baratovite
WebMineral: View Baratovite
Mindat: View Baratovite

SOLD

Beryl

with Cassiterite - #PD34910

$35.00 - Sold
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Locality: Orchard quarry, Buckfield, Oxford Co., Maine, United States
Formula: Be₃Al₂Si₆O₁₈
Availability: Sold
Size: 9 x 5.5 x 6.5 cm - Sm Cabinet
Tagged: beryllium , pegmatite

A typical example of pegmatite showing green beryl crystals to 3cm long suspended in albite matrix with cassiterite crystal grains to 6mm.

Beryl

Formula: Be₃Al₂Si₆O₁₈
Crystal System: Hexagonal
Crystal Habit: Crystalline - Coarse, Prismatic, Columnar
Cleavage: Imperfect, None, None
Luster: Vitreous - Resinous
Color: green, blue, yellow, colorless, pink
Streak: white
Class: Hexagonal - Dihexagonal Dipyramidal
Fracture: Brittle - Conchoidal
Hardness: 7.5-8

Collection: Phillips Collection

Mineralpedia: View Beryl
On Dakota Matrix: Previously Sold Beryl
On Dakota Matrix: Other Available Beryl
WebMineral: View Beryl
Mindat: View Beryl

SOLD

Beryl

#34930

$45.00 - Sold
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Locality: Zimmerman pegmatite, Copper Mtn dist., Fremont Co., Wyoming, United States
Formula: Be₃Al₂Si₆O₁₈
Availability: Sold
Size: 11 x 10 x 7 cm - Cabinet
Tagged: pegmatite

This specimen exemplifies the characteristics of beryl from a pegmatite. As is typical of outer zone beryl crystals, this specimen shows a tapering in the long dimension probably a result of inward growth in the direction in which the pegmatite forms. I don't usually sell broken specimens like this, but it is a marvelous teaching example showing the crystal habit and properties such as the basal (c-axis) cleavage.

At one time pegmatites were the major source of beryllium. These days beryllium is mined from non-pegmatitic sources namely the bertrandite epithermal deposits of Spor Mountain and Gold Hill deposits of Utah and Seward Peninsula in Alaska.

Beryllium is used in computer and telecommunications products, in aerospace and defense applications, appliances, and electronics.