Potassic-fluoro-hastingsite
(Fluoro-potassic-hastingsite)

Discovered in 2005; IMA status: Valid (IMA approved 2005)

Chemistry

Chemical Formula:

KCa₂(Fe₄²⁺Fe³⁺)(Al₂Si₆O₂₂)(F,OH)₂

Potassium Calcium Iron Aluminum Silicate Floride Hydroxide

Molecular Weight:

947.86 gm

Composition:

Potassium

4.12 %

K

4.97 %

K₂O

Calcium

8.46 %

Ca

11.83 %

CaO

Magnesium

5.13 %

Mg

8.50 %

MgO

Aluminum

5.69 %

Al

10.76 %

Al₂O₃

Iron

17.68 %

Fe

15.16 %

FeO / 8.42 % Fe₂O₃

Silicon

17.78 %

Si

38.03 %

SiO₂

Oxygen

37.13 %

O

Fluorine

4.01 %

F

4.01 % 

  -  %

F

-1.69 %

 -O=F₂

100.00 %

100.00 %

= TOTAL OXIDE

Classification

Mineral Classification:

Silicates (Germanates)

Strunz 8th Ed. ID:

8/F.10-145

Nickel-Strunz 10th Ed. ID:

9.DE.15

9 : SILICATES (Germanates)
D : Inosilicates
E : Inosilicates with 2-periodic double chains, Si₄O₁₁; Clinoamphiboles

Related to:

Hastingsite Root Name Group. Calcium Amphibole Subgroup. w(OH, F, Cl)-dominant Amphibole Group. Amphibole Supergroup.

Members of Group:

Hastingsite Root Name Group: Fluoro-hastingsite, Hastingsite, Magnesio-fluoro-hastingsite, Magnesio-hastingsite, Potassic-chloro-hastingsite, Potassic-fluoro-hastingsite, Potassic-hastingsite, Potassic-magnesio-hastingsite 

Members of Sub-Group:

Calcium Amphibole Subgroup: Cannilloite Root Name, Edenite Root Name, Hastingsite Root Name, Hornblend Root Name, Pargasite Root Name, Sadanagaite Root Name, Tremolite-Actinolite Series, Tschermakite Root Name

Varieties:

None

Synonyms:

IMA2005-006, Fluoro-potassic-hastingsite

Crystal Data

Crystallography:

Monoclinic - Prismatic

Crystal Habit:

Crystals prismatic; in compact aggregates to 1 cm

Twinning:

None

Physical Properties

Cleavage:

Perfect on {110}, intersecting at 56°

Fracture:

Concoidal, sub-concoidal

Tenacity:

Brittle

Moh's Hardness:

6.0

Density:

3.289 (g/cm³)

Luminescence:

None

Radioactivity:

Barely Detectable; GRapi = 58.40 (Gamma Ray American Petroleum Institute Units)

Optical Properties

Color:

Black, dark greenish black on thin edges

Transparency:

Transparent to translucent

Luster:

Vitreous, sub-vitreous

Refractive Index:

1.668 - 1.698  Biaxial  ( - )

Birefringence:

0.030

Dispersion:

Moderate to strong; r

Pleochroism:

Strong; X = bluish green; Y = greenish to brownish green; Z = blue to light blue

Occurances

Geological Setting:

A product of potassium-halogen metasomatism of a hastingsite and diopside-bearing rock. A magnetite-rich iron ore deposit hosted by Proterozoic metamorphic rocks.

Common Associations:

Magnetite, Diopside, Enstatite, Pyrrhotite, Chalcopyrite, Pyrite, Phlogopite

Common Impurities:

Na, Mg, Cl

Type Locality:

Greenwood mine (Patterson mine), Town of Tuxedo, Orange County, New York, USA

Year Discovered:

2005; IMA approved 2005, IMA redefined and renamed 2012

View mineral photos:

Potassic-fluoro-hastingsite Mineral Photos and Locations

Unusual Gem Categories

Black Gems

More Information

Mindat.org 
Webmineral.com

Potassic-fluoro-hastingsite is a rare member of the Calcium Amphibole Subgroup of minerals that also includes Actinolite, Pargasite, Sadanagaite, Tremolite and Tschermakite. Potassic-fluoro-hastingsite is very rare and obscure mineral and only found in one place in the world - the Greenwood Mine in the Town of Tuxedo, Orange County, New York, USA. It is rarely found in mineral collections and even rarer as a faceted gem! It is black with vitreous luster and is barely radioactive due to its potassium content.

Potassic-fluoro-hastingsite was discovered in 2005 in the tailings dump of the Greenwood (Patterson) iron mine. The mine, located in Hudson Highlands, in Harriman State Park, Town of Tuxedo, Orange County, New York, USA, was first opened in 1838, and was a source of iron during the Civil War. It was last worked in 1880.

This mineral was originally named Fluoro-potassic-hastingsite in 2009 by Marian V. Lupulescu, John Rakovan, M. Darby Dyer, George W. Robinson, and John M. Hughes for its chemical relationship to Hastingsite. But it was redefined and renamed in 2012 by the Amphibole Subcomittee of the Commission on New Minerals, Nomenclature and Classification (CNMNC). The new IMA approved name is Potassic-fluoro-hastingsite following the principle that the various prefixes to the root name are listed in the order they occur in the formula.

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