Liroconite
Rarity
Discovery
Habit & Form
Descriptions
Locations
Cornish Minerals
Links
About us
Clinoclase

Clinoclase in another very rare secondary copper arsenate found in the oxidation zone of copper deposits, and is sometimes found associated with Liroconite. 

It has only been found in a few sites in the world, some of the most well known being Wheal Gorland, Gwennap, Cornwall in the UK, its type locality, and Majuba Hill, Pershing County, Nevada, USA. Both have yielded some wonderful Clinoclase display specimens. Both these mines are now closed, and good well crystallised specimens are only rarely available and command a high price. 

Clinoclase - Wheal Unity, Gwennap, Cornwall, UK

Dark blue-black lustrous crystalline 4mm aggregates of Clinoclase, known as "beetle ore".

Clinoclase Discovery

Clinoclase was first found in the old copper mines of Cornwall, at the same time as Liroconite with which it was often associated. The main source of Clinoclase were the Wheal Gorland, Wheal Unity and Wheal Muttrell mines in the Gwennap area near St Day. It was first given the name Clinoclase by Breithaupt in 1830, the name coming from the Greek Klineis "to incline" and Klas "to break" after its oblique cleavage. The name expresses the fact that the basal cleavage is inclined to the faces of the oblique prism.  Variations of this name include Clinoclasita, Clinoclasit, Clinoclasite, Klinoklas and Klinoclas. It has also been given a number of other names: Oblique Prismatic Arseniate of Copper, Abichit (and Abichita, Abichite, Aphanese, Aphanesit, Aphanesite, Aphanesita), Siderochalcit (and Siderochalcita, Siderochalcite), and Strahlenkupfer.

Clinoclase and Liroconite  - Wheal Gorland, Gwennap, Cornwall, UK

Clinoclase Habit & Form

Clinoclase is very distinctive and has a totally different colour and crystal shape to Liroconite.  The Cornish arsenates of copper were studied in the early 1800's by the Comte de Bournon, who was led to remark that "Nature has established very remarkable differences between the arseniates of copper." While the chemistry of the copper arsenates such as Liroconite, Clinoclase, Olivenite, Cornwallite and Chalcopyllite, is fairly similar, their external appearance is radically different.  This can lead to some very beautiful mineral specimens, with the various copper arsenates contrasting with each other in form and colour.

Clinoclase and Liroconite - Wheal Gorland, Gwennap, Cornwall, UK

Clinoclase has a very dark blue to black colour, with a greenish tint, except sometimes on broken surfaces where the colour is lighter.

Typically the crystal surfaces are highly lustrous.  Clinoclase crystals tend to be acicular or tabular with small modifications to the faces.  Sometimes it forms what the old Cornish miners referred to as "Beetle ore".  These are spherical rounded aggregates or radiating balls with a crystalline surface that resemble dark blue-black beetles. Such balls reached 2cm or more in size in Wheal Gorland and Wheal Unity in Cornwall.

Clinoclase and Cornubite - Wheal Gorland, Gwennap, Cornwall, UK.    Peter Golley colln.

Clinoclase - Wheal Unity, Gwennap, Cornwall, UK

A nest of long acicular Clinoclase crystals to 4mm on Quartz.  Collected in 1977 by Richard Barstow

Clinoclase - Wheal Unity, Gwennap, Cornwall, UK

Long acicular Clinoclase crystals to 4mm on Quartz.  Collected in 1977 by Richard Barstow. Same specimen as above. 

Clinoclase - Wheal Unity, Gwennap, Cornwall, UK

Clinoclase Chemical Characteristics

Chemical formula

Cu3AsO4(OH)3

Chemistry

Copper Arsenate Hydroxide

Class

Phosphates

Subclass

Arsenates

Dana class

41.3.1.1

Strunz class

7/B.13-20

Composition:

Copper         50.09%

 

Arsenic          19.69%

 

Hydrogen       0.79%

 

Oxygen         29.43%

Chemical indicator

Slightly soluble in hydrochloric acid

 

 

Clinoclase - Gwennap, Cornwall, UK

"Very dark green arseniate of copper cryd., a very scarce variety, Cornwall" - Robert Fergusson collection and description.

Clinoclase Physical Characteristics

Colour

Very dark blue-black, Blackish blue-green, Dark greenish black

Streak

Bluish green

Lustre

Vitreous - pearly

Luminescence

None

Transparency

Translucent

Optical Data

Biaxial (-), a=1.73, b=1.87, g=1.91, bire=0.1800, 2V(Calc)=52, 2V(Meas)=30. Dispersion relatively strong.

Hardness

2.5 - 3

Specific Gravity

4.19 to 4.40, average 4.29

Crystal System

Monoclinic, 2/m

Axial Ratios

a:b:c = 1.917 : 1 : 1.124

Cell Dimensions

a = 12.4, b = 6.47, c = 7.27, Beta=99.58

X-Ray Diffraction

by Intensity(I/Io): 3.587(1), 3.139(0.25), 7.21(0.2)

Cleavage

Good in one direction

Fracture

Lamellar.  Flat surfaces fracture in an uneven pattern.

Associated Minerals

Liroconite, Cornwallite, Olivenite, Chalcopyllite, Malachite, Azurite, Cuprite, Adamite, Brochantite

Best Field Indicators

Colour, streak, crystal habit, associated minerals, and density

Clinoclase - Wheal Gorland, Gwennap, Cornwall, UK  Acicular Clinoclase crystals to 3mm on Quartz

Clinoclase and Cornubite - Wheal Gorland, Gwennap, Cornwall, UK    Col. Musee Bally

Copyright (C) 2003-2008 David Aubrey-Jones.  All rights reserved.  No part of this Web site and its contents may be reproduced in any form without the written permission of the author.

[Liroconite] [Rarity] [Discovery] [Habit & Form] [Descriptions] [Locations] [Cornish Minerals] [Links] [About us]