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Habit & Form

Liroconite - Wheal Gorland, Gwennap, Cornwall, UK

"Transparent Crystals of Copper Ore in double four sided Pyramids of a bright blue colour the largest crystal 9/10 of an Inch on one edge from Wheal Gorland r.r.r. (very rare)"  Rashleigh collection and description.

This specimen was added to the famous Rashleigh collection of minerals in 1808, and can be seen in the Royal Cornwall Museum in Truro, UK. 

Liroconite colour is variable

The colour of the Liroconite varies from sky-blue to turquoise-blue through to verdigris-green, which may be related to minor differences in chemical composition. Its streak colour is much paler as does its powdered form, as its name suggests. It is also sensitive and can occasionally fade to a bluish-white and exceptionally even disintegrate.

Liroconite has a very unusual crystal shape

The chemical formula of Liroconite is Cu2Al[(OH)4/AsO4].4H20. It forms pseudotetragonal to flat distorted pyramidal crystals.  Crystals to two centimetres diameter and greater were found when Liroconite was first discovered in Cornwall (1780-1790).  In 1808 the largest known crystal, reaching 3.5cm, was added to the famous Rashliegh collection. This can be seen today in the County museum of Cornwall in Truro in the UK, and is shown in the photo.

Liroconite - Wheal Gorland, Gwennap, Cornwall, UK

Liroconite crystals of a deep green colour, some with a sky blue core.

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

An unusual specimen with both sky blue and green Liroconite crystals together with inky blue Clinoclase.   Ex. Peter Golley collection.

Liroconite Crystal Habit

Liroconite crystals have an unusual shape, and are composed of the sides of a four faced prism, and four faces of two monoclinic domes. They often appear to have an eight faced tetragonal bipyramidal form.

The old name of "lenses ore" refers to the typical elliptical shape, with crystals frequently appearing bent with rounded edges.

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

Blue Liroconite crystals sharply defined against a backround of white Strashimirite

Liroconite Chemical Characteristics

Chemical formula

Cu2Al(AsO4)(OH)4 - 4H2O

Chemistry

Hydrated Copper Aluminium Arsenate Hydroxide

Class

Phosphates

Subclass

Arsenates

Dana class

42.2.1.1

Strunz class

VII/D.20-40

Composition:

Aluminium        6.23%

 

Copper         29.35%

 

Arsenic          17.30%

 

Hydrogen       2.79%

 

Oxygen         44.33%

Chemical indicator

Does not react with acid

Liroconite Physical Characteristics

Colour

Light blue to sky blue to blue-green to green

Streak

Pale blue (as its Greek name would suggest)

Lustre

Vitreous resinous

Luminescence

None

Transparency

Transparent to translucent

Optical Data

Biaxial (-), a=1.612, b=1.652, g=1.675, bire=0.0630, 2V(Calc)=72, 2V(Meas)=67. Dispersion none.

Hardness

2 to 2.5

Specific Gravity

2.90 to 3.00, average 2.95

Crystal System

Monoclinic Prismatic

Axial Ratios

a:b:c =1.6719:1:1.3064

Cell Dimensions

a = 12.665, b = 7.575, c = 9.896, Z = 4; beta = 91.25 V = 949.17 Den(Calc)= 3.03

X-Ray Diffraction

by Intensity(I/Io): 6.52(1), 6.03(0.8), 3.005(0.5),

Cleavage

Poor in two directions parallel to the prism faces. (100) Indistinct, (011) Indistinct.

Fracture

Uneven to sub-conchoidal, fractures are characterised by semi-curving surfaces.

Associated Minerals

Clinoclase, Olivenite, Parnuite, Strashimirite, Chalcopyllite, Malachite, Azurite, Cuprite

Best Field Indicators

Crystal habit, associated minerals, streak and colour

Liroconite - Wheal Gorland, Gwennap, Cornwall, UK

A solid face of lustrous blue Liroconite crystals forming a lovely display about 4cm across

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.

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