ClassicGems.net

 

Neptunite

 

Neptunite

 

Discovered in 1893; IMA status: Valid (pre-IMA; Grandfathered)

 

Chemistry

 

 

Chemical Formula:

KNa2Li(Fe2+,Mn2+)2Ti2Si8O24

 

Potassium Sodium Lithium Iron Manganese Titanium Silicate

Molecular Weight:

907.69 gm

Composition:

Potassium

4.31 %

K

5.19 %

K2O

 

Sodium

5.07 %

Na

6.83 %

Na2O

 

Lithium

0.76 %

Li

1.65 %

Li2O

 

Titanium

10.55 %

Ti

17.60 %

TiO2

 

Manganese

3.03 %

Mn

3.91 %

MnO

 

Iron

9.23 %

Fe

11.87 %

FeO

 

Silicon

24.75 %

Si

52.96 %

SiO2

 

Oxygen

42.30 %

O

 

 

 

 

100.00 %

 

100.00 %

= TOTAL OXIDE

 

 

Classification

   

   

Mineral Classification:

Silicates

Strunz 8th Ed. ID:

8/F.37-10

Nickel-Strunz 10th Ed. ID:

9.EH.05

 

9 : SILICATES (Germanates)
E : Phyllosilicates
H : Transitional structures between phyllosilicate and other silicate units

Related to:

Neptunite Group. Isostructural with Manganoneptunite. Manganoneptunite-Neptunite Series.

Members of Group:

Neptunite Group: Magnesioneptunite, Manganoneptunite, Neptunite

Varieties:

None

Synonyms:

Carlosite, Ferroneptunite, ICSD 71360, PDF 43-677

 

 

Crystal Data

   

   

Crystallography:

Monoclinic - Domatic

Crystal Habit:

As prismatic crystals, to 7.5 cm, with {110} prominent, typically with square cross sections, may be curved or twisted.

Twinning:

Interpenetrant on {301}.

 

 

Physical Properties

   

 

Cleavage:

Perfect on {110}

Fracture:

Conchoidal

Tenacity:

Brittle

Mohs Hardness:

5.0 - 6.0

Density:

3.19 - 3.23 (g/cm3)

Luminescence:

None

Radioactivity:

Not Radioactive

Other:

Piezoelectric

 

 

Optical Properties

   

   

Color:

Black; deep blood red to red-brown in thin fragments

Transparency:

Opaque to nearly opaque

Luster:

Vitreoius

Refractive Index:

1.690 - 1.736  Biaxial ( + )

Birefringence:

0.029 - 0.045

Dispersion:

r < v; strong to extreme

Pleochroism:

Visible; X = pale yellow; Y = yellow-orange; Z = red-orange to red-brown

 

 

Occurances

   

   

Geological Setting:

In natrolite veins cutting a glaucophane schist inclusion in a serpentinite body (San Benito County, California, USA).

Common Associations:

Eudialyte, Arfvedsonite, Aegirine (Narssârssuk, Greenland); Natrolite, Benitoite, Joaquinite-(Ce) (San Benito County, California, USA); Nordite-(La), Lomonosovite, Sodalite, Ussingite (Kola Peninsula, Russia).

Common Impurities:

Ca

Type Locality:

Narsaarsuk pegmatite (Narssârssuk pegmatite), Narsaarsuk Plateau, Igaliku (Igaliko), Narsaq, Kujalleq, Greenland

Year Discovered:

1893

View mineral photos:

Neptunite mineral photos and locations

 

 

Unusual Gem Categories

   

   

 

Black Gems, Piezoelectric Gems

 

 

More Information

   

   

 

Mindat.org
Webmineral.com

 

 

Neptunite is a rare lithium titanium silicate mineral that is popular as mineral specimens but rarely available as faceted gems. Neptunite forms shiney black, elongated, prismatic crystals which are usually square in cross section with pointed terminations. It is opaque and black except in very small fragments. Thin fragments may be dark, blood red to dark, brownish red. Neptunite is usually available only as beautiful mineral specimens set in a matrix of pure white Natrolite along with blue Benitoite crystals and rarely with orangish brown Jaoquinite-(Ce) crystals. Although there are several locations throughout the world to find Neptunite crystals, the most well known source of Neptunite is at the now closed Benitoite Gem Mine, San Benito County, California, USA.

Neptunite is one of the unusual minerals that exhibit the piezoelectric effect. Piezoelectricity is the ability of some mineral crystals to generate a voltage in response to applied mechanical stress such as an external pressure. Piezoelectricity was discovered in 1880 by French physicists, brothers Jacques and Pierre Curie.

Neptunite was named in 1893 by Swedish mineralogist Gustav Flink (1848-1931) for Neptune, the Roman god of the sea. This name was given because of Neptunite's close association at its type locality at Narssârssuk, Greenland with the mineral Aegirine, named for Ægir, god of the sea and king of all sea creatures in Norse mythology. Aegirine was named in 1834 by Norwegian priest and mineralogist Hans Morten Thrane Esmark (1801-1882).

Neptunite distribution: from Narssârssuk, Iglunguak, and the Ilímaussaq intrusion, Greenland. In the Inagli massif, 30 km west of Aldan, Yakutia, and in the Khibiny and Lovozero massifs, Kola Peninsula, Russia. From the Khan-Bogdinskii granitic massif, Gobi, Mongolia. In the Dara-i-Pioz massif, Alai Range, Tien Shan, Tajikistan. From Barnavave, near Carlingford, County Louth, Ireland. At Mont Saint-Hilaire, Quebec, and Seal Lake, Labrador, Newfoundland, Canada. In the USA, splendid crystals from the Benitoite Gem mine and Mina Numero Uno, San Benito County, California, and at Point of Rocks, Colfax County, New Mexico. From near Woodsreef, New South Wales, Australia.

Neptunite gems for sale:

Neptunite-001

Gem:

Neptunite

Stock #:

NEPT-001

Weight:

0.7560 ct

Size:

7.00 x 5.14 x 2.36 mm

Shape:

Oval Cabochon

Color:

Black

Clarity:

Opaque

Origin:

San Benito County, California, USA

Treatment:

None (natural)

Price:

SOLD (but we have others)

Pictures are of the actual gem offered for sale.
Gem images are magnified to show detail.

Neptunite-001

An unusual gem from a very famous Benitoite locality.

 

 


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