amorphous Phyllosilicates

Chrysocolla

Formula (Cu,Al)2H2Si2O5(OH)4.nH2O

Crystal Structure

CDL Notation

 #! Species: Chrysocolla (hydrous copper aluminosilicate)
#! System: Amorphous (cryptocrystalline)
#! Habit: Massive botryoidal to earthy; blue-green
amorphous[waxy]:{botryoidal}

Crystal System amorphous

Point Group none

Crystal Forms (1)

{botryoidal}

Quick Facts

Hardness

2.5

Specific Gravity

1.93

Refractive Index

1.46

Optical Character

Isotropic (amorphous) to anomalous in cryptocrystalline

Physical Properties

Crystal System: amorphous
Hardness (Mohs): 2.5
Specific Gravity: 1.93
Cleavage: None
Fracture: Conchoidal
Lustre: Waxy to vitreous (gem silica vitreous; earthy in massive low-quality)

Optical Properties

Refractive Index: 1.46
Optical Character: Isotropic (amorphous) to anomalous in cryptocrystalline
Pleochroism: None

Characteristics

Colours

Blue-green (most common; Cu2+ idiochromatic)Turquoise-blueCyanRarely pure blue or pure green

Localities

Peru (Lily mine, Pisco region; gem silica — highest gem quality blue chalcedony with chrysocolla)Arizona, USA (Globe-Miami district; gem silica and chrysocolla-malachite)Chile (Atacama; copper deposits)Democratic Republic of Congo (Katanga; massive material)Israel (Timna / Eilat stone; chrysocolla + turquoise + malachite mix)

Common Inclusions

Massive; inclusions not relevant for identification[object Object]

Known Treatments

Stabilisation with resin (common for soft material)Polymer impregnation

Crystal Forms

botryoidalmassiveearthy

Diagnostic Features

Very low SG 1.93-2.40 (pure material; much lower than turquoise 2.60-2.90); waxy lustre; Cu2+ blue-green colour (idiochromatic); spot RI typically ~1.50 (vs turquoise ~1.61-1.65); stabilised and polymer-impregnated material common

Notes

Hydrous copper aluminium silicate; amorphous to cryptocrystalline. Crystal system set to amorphous per database convention (same as opal). Structural and chemical characterisation confirmed by Frost & Xi 2013, Vibrational Spectroscopy 63:33-38 (DOI 10.1016/j.vibspec.2012.10.001) [VERIFIED]: "Chrysocolla...is variably described as amorphous or cryptocrystalline." Hardness extremely variable (2.5-7); gem silica (quartz-impregnated variety) reaches 6-7. Cu2+ idiochromatic blue-green colour. Gem silica = blue-green chalcedony with interstital chrysocolla; highest gem quality from Peru. Acid-sensitive (dissolves in HCl). Water-sensitive (dehydration may cause cracking). Constants (SG, RI) from Read 7th ed. (DOI 10.4324/9780080507224) [PARTIALLY_SUPPORTED].