Kröhnkite
Current inventory:  0 gems
 

  
Kröhnkite was named to honor B. Kröhnke, who provided the first analysis of the mineral.

Discovered in 1876;  IMA status: Valid (pre-IMA; Grandfathered)

Chemistry

Chemical Formula:

Na₂Cu(SO₄)₂ • 2H₂O

Hydrated Sodium Copper Sulfate

Molecular Weight:

337.68 gm

Composition:

Sodium

13.62 %

Na

18.35 %

Na₂O

Copper

18.82 %

Cu

21.19 %

Cu₂O

Hydrogen

1.19 %

H

10.67 %

H₂O

Sulfur

18.99 %

S

47.42 %

SO₃

Oxygen

47.38 %

O

100.00 %

97.63 %

= TOTAL OXIDE

Classification

Mineral Classification:

Sulfates

Strunz 8th Ed. ID:

6/C.16-10

Nickel-Strunz 10th Ed. ID:

7.CC.30

7 : SULFATES (selenates, tellurates, chromates, molybdates, wolframates)
C : Sulfates (selenates, etc.) without additional anions, with H₂O
C : With medium-sized and large cations

Related to:

Roselite Group.

Members of Group:

Roselite Group: Brandtite, Kröhnkite, Roselite, Rruffite, Wendwilsonite.

Varieties:

None

Synonyms:

Kroehnkite, Krömkite, Krönnkite, Salvadorite (of Herz)

Crystal Data

Crystallography:

Monoclinic - Prismatic

Crystal Habit:

Crystals are pseudo-octahedral, equant to short prismatic along [001] or [100], to 7 cm; typically they exhibit {110}, {011}, {010}, {021}, {111}, with over two dozen more forms recorded. In crusts and aggregates, granular, massive.

Twinning:

Common on {101}, may be heart-shaped.

Physical Properties

Cleavage:

Perfect on {010}; poor on {101}

Fracture:

Conchoidal

Tenacity:

Brittle

Moh's Hardness:

2.5 - 3.0

Density:

2.90 (g/cm³)

Luminescence:

None

Radioactivity:

Not Radioactive

Other:

Readily soluble in water.

Optical Properties

Color:

Sky-Blue to pale Blue or Greenish Blue, becoming Green and opaque on exposure; pale Blue to Colorless in transmitted light.

Transparency:

Transparent to Translucent

Luster:

Vitreous

Refractive Index:

1.544 - 1.601  Biaxial ( - ) 

Birefringence:

0.057

Dispersion:

Weak

Pleochroism:

None

Occurances

Geological Setting:

An uncommon secondary mineral formed in the oxidized zone of copper deposits, typically in very arid climates.

Common Associations:

Atacamite, Blödite, Chalcanthite, Antlerite, Natrochalcite (Chuquicamata, Chile).

Common Impurities:

None

Type Locality:

Chuquicamata Mine, Chuquicamata District, Calama, El Loa Province, Antofagasta Region, Chile

Year Discovered:

1876

View mineral photos:

Kröhnkite Mineral Photos and Locations

More Information

Mindat.org
Webmineral.com

Kröhnkite is a rare hydrated copper sulfate mineral that is very soft with a Mohs hardness of 2.5 - 3.0. Hydrated means that it contains water in its chemical formula meaning it is prone to dehydration and must be kept protected. It is also readily soluble in water. Kröhnkite is an uncommon secondary mineral formed in the oxidized zone of copper deposits, typically in very arid climates. It is found in colors of sky-blue to greenish blue becoming green and opaque on exposure. Faceted gems are extremely rare but very attractive due to its wonderful colors.

Distribution: In Chile, abundantly and in large crystals from Chuquicamata, at Quetena, west of Calama, and at Collahuasi, Antofagasta; from El Cobre de Mejillones and in the Incahuasi district, Atacama. In Wheal Hazard, St. Just, Cornwall, England. From the Recsk copper deposit, Mátra Mountains, Hungary. At Capo Calamita, Elba, Italy. From Broken Hill, New South Wales, Australia.
 

  
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