Arrojadite-(KFe)
Current inventory:  0 gems
 

  
Arrojadite was named to honor Miguel Arrojado Ribeiro Lisbôa (1872–1932), a Brazilian engineer, geologist and geographer. He gained international renown for his studies of manganese and monazitic sands.

Discovered in 1925; IMA status: Valid (pre-IMA; Grandfathered)

Chemistry

Chemical Formula:

KNa₄Ca(Fe²⁺,Mn²⁺)₁₄Al(PO₄)₁₂(OH)₂

Potassium Sodium Calcium Iron Manganese Aluminum Phosphate Hydroxide  

Molecular Weight:

2,033.08 gm

Composition:

Potassium

1.92 %

K

2.32 %

K₂O

Sodium

4.52 %

Na

6.10 %

Na₂O

Calcium

1.97 %

Ca

2.76 %

CaO

Magnesium

2.39 %

Mg

3.96 %

MgO

Manganese

10.81 %

Mn

13.96 %

MnO

Aluminum

1.33 %

Al

2.51 %

Al₂O₃

Iron

19.23 %

Fe

24.74 %

FeO

Phosphorus

18.28 %

P

41.89 %

P₂O₅

Hydrogen

0.12 %

H

1.11 %

H₂O

Oxygen

38.95 %

O

Fluorine

0.47 %

F

0.47 %

F

—

 —  %

F

-O=F₂

100.00 %

99.61 %

= TOTAL OXIDE

Classification

Mineral Classification:

Phosphates

Strunz 8th Ed. ID:

7/B.20-10

Nickel-Strunz 10th Ed. ID:

8.BF.05

8 : PHOSPHATES, ARSENATES, VANADATES
B : Phosphates, etc., with additional anions, without H₂O
F : With medium-sized and large cations, (OH, etc.):RO₄< 0.5:1

Related to:

Arrojadite Group. Arrojadite-(KFe)-Dickinsonite-(KMnNa) Series

Members of Group:

Arrojadite Group: Arrojadite-(BaFe), Arrojadite-(BaNa), Arrojadite-(KFe), Arrojadite-(KFeNa), Arrojadite-(KNa), Arrojadite-(NaFe), Arrojadite-(PbFe), Arrojadite-(SrFe), Dickinsonite-(KMnNa), Ferri-arrojadite-(BaNa), Fluorarrojadite-(BaFe), Fluorarrojadite-(KNa), Fluorarrojadite-(NaFe) 

Varieties:

None

Synonyms:

Arrojadite, Headdenite

Crystal Data

Crystallography:

Monoclinic - Domatic

Crystal Habit:

As cleavable masses, to 15 cm

Twinning:

None

Physical Properties

Cleavage:

Good on {100}, poor on {102}

Fracture:

Uneven/Irregular to Subconchoidal

Tenacity:

Brittle

Moh's Hardness:

5.0

Density:

3.50 - 3.60 (g/cm³)

Luminescence:

None

Radioactivity:

Barely Detectable; GRapi = 26.90 (Gamma Ray American Petroleum Institute Units)

Optical Properties

Color:

Dark green, bottle-green, yellowish green, brownish yellow,

Transparency:

Translucent

Luster:

Vitreous to greasy

Refractive Index:

1.664 - 1.675  Biaxial ( + )

Birefringence:

0.011

Dispersion:

Strong, r < v

Pleochroism:

Visible; X = colorless; Y = colorless to pale green; Z = pale yellow-green

Occurances

Geological Setting:

A high-temperature (~ 800°C) primary mineral in granite pegmatites.

Common Associations:

Graftonite, Cassiterite, Spodumene, Beryl, Muscovite (Nickel Plate mine, South Dakota, USA)

Common Impurities:

n/a

Co-Type Localities:

• Serra Branca pegmatite, Pedra Lavrada, Borborema mineral province, Paraíba, Brazil
• Nickel Plate Mine, Keystone, Keystone District, Pennington Co., South Dakota, USA

Year Discovered:

1925

View mineral photos:

Arrojadite Mineral Photos and Locations

More Information

Mindat.org
Webmineral.com

Arrojadite-(KFe) is a rare phosphate mineral. It was named to honor Miguel Arrojado Ribeiro Lisbôa (1872–1932), a Brazilian engineer, geologist and geographer. He gained international renown for his studies of manganese and monazitic sands. In 2005 Arrojadite's name was changed to Arrojadite-(KFe) by the International Mineralogical Association (IMA) as part of the revision of the nomenclature of the Arrojadite Group to distinguish it chemically from the other members of the group. Many of the other members of the group have the same root name with various suffixes added to denote their unique chemical structures. The following are some of the members of the Arrojadite Group: Arrojadite-(BaFe), Arrojadite-(BaNa), Arrojadite-(KFe), Arrojadite-(KFeNa), Arrojadite-(KNa), Arrojadite-(NaFe), Arrojadite-(PbFe), Arrojadite-(SrFe).

Arrojadite is rarely, if ever, found as transparent crystals large enough for faceting. It is typically found as translucent to opaque, cleavable masses. Gems have been faceted from this material purely as a rare collector's gem. The best specimens for mineral collectors come from a find in 2001 at the Big Fish River–Rapid Creek area, Dawson Mining District, Yukon Territory, Canada. This source has produced some of the richest examples of Arrojadite ever found.

Distribution: In Brazil, from the Serra Branca pegmatite, 13 km south of Pedra Lavrada, Picuí, Paraíba; in the Énio pegmatite mine, northeast of Galiléia, and the Sapucaia pegmatite mine, about 50 km east-southeast of Governador Valadares, Minas Gerais. In the USA, in New Hampshire, from the G.E. Smith mine, Newport, Sullivan County, and at the Rice, Nancy #2, and Palermo #1 mines, near North Groton, Grafton County; in South Dakota, from the Nickel Plate and White Cap mines, near Keystone, Pennington County, and in the Victory mine, four km northeast of Custer, Custer County. From the Big Fish River–Rapid Creek area, Yukon Territory, Canada. In the Mangualde pegmatite, near Mesquitela, Portugal. From Glenbuchat, Aberdeenshire, Scotland. In the Norrö pegmatite, on Rånö Island, Sweden. At Sidi-Bou-Kritcha, Morocco. In Zimbabwe, from Ruwanzi Ranch, Karoi East, Miami, and on the Star Twin, Pearl and Chiwya claims, Urungwe district. In the Buranga pegmatite, near Gatumba, Rwanda.
 

  
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