Chalcedony

minerals

fluorite

baryte

aragonite

Images
Chalcedony is a variety of quartz.
Formula: SiO2 tectosilicate (framework silicate)

Varieties

Agate is a distinctly banded fibrous variety of chalcedony
Jasper is an opaque to slightly translucent, generally red or brown variety of chalcedony, containing inclusions of hematite

Specific gravity: 2.6
Hardness: 6½; to 7
Streak: White
Colour: Colourless, white, gray, blue, any colour due to embedded minerals; multicoloured specimens not uncommon.
Solubility: Insoluble in hydrochloric, sulphuric and nitric acid
Environments:

Volcanic igneous environments
Sedimentary environments
Metamorphic environments
Hydrothermal environments

Chalcedony is deposited from aqueous solutions, and is frequently found lining or filling cavities in volcanic rocks, as crusts in epithermal (low temperature) to mesothermal (medium temperature) hydrothermal veins, as a constituent of silica-rich marine sedimentary rocks, and as nodular concretions and layers in limestone and marl.

Localities

At Jalgaon, Maharashtra province, India, chalcedony pseudomorphs after calcite on chalcedony have been found (KL p255).

At Trestia, south of Cavnic, Muramures, Romania, chalcedony pseudomorphs after fluorite have been found (KL p257).

At Mkobola district, Mpumalanga province, South Africa, a chalcedony pseudomorph after a quartz Japanese twin has been found (KL p258).

Near Fruita, Mesa county, Colorado, USA, pseudomorphs of chalcedony variety agate after baryte have been found (KL p261).

At the Big Bend area, Brewster county, Texas, USA, chalcedony pseudomorphs after aragonite have been found (KL p256).

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