Chalcedony

Chalcedony

Chalcedony
 

 

 

 

 

 

 

 

 

Composition: Silicon dioxide (SiO2)

Synonyms/Varieties:
 

Agate
Amethyst
Aventurine
Bloodstone
Cairngorm Stone
Carnelian
Chalcedony
Chert
Chrysoprase
Citrine
Flint
Jasper
Milky Quartz
Prase
Rock Crystal
Rose Quartz
Rutilated Quartz
Sardonyx
Smoky Quartz
Tiger-eye
 
 

Physical Properties:
Color: White, colorless, gray, yellow to orange-yellow, purple, violet, pink, gray-brown to brown, black
Streak: White; faintly tinted in color varieties
Luster: Vitreous, greasy, waxy
Hardness: 7
Tenacity: Brittle, tough
Specific Gravity: 2.65-2.66
Cleavage: Generally none

Crystallography:
System: Hexagonal
Twinning: Common
Habit: Crystals are short to long prismatic, pyramidal, distorted, twisted, bent, skeletal, and as druses. Aggregates are massive, coarse to granular, stalactitic, concretionary, and as sand.

General Information:
Chalcedony is the name applied to microfibrous masses of quartz that have a waxy luster. The individual quartz fibers are so small that they can be seen only with special apparatus and a high-power microscope. Minute water-filled pores between the tiny fibers result in masses of chalcedony having lower specific gravities than quartz, and also are probably the cause of chalcedony having a waxy luster instead of being vitreous like typical quartz. However, the hardness is 7, as is that of vitreous coarsely-crystalline quartz. Pure chalcedony is colorless, white, or grayish, and is translucent or transparent. However, it is commonly brown, red, yellow, green, bluish, or dark gray because of small amounts of finely divided colored minerals disseminated among the quartz fibers. Chalcedony is relatively abundant in California. It is the predominant constituent of chert, a common rock in the state, and occurs lining or filling fissures and other cavities in various rocks, particularly volcanic rocks. When deposited in wide fissures, masses of chalcedony often assume globular or stalactitic forms. Chalcedony is also found in many places where it has replaced other materials, commonly retaining the form and texture of objects replaced. An example of the latter is petrified wood. The principal use of chalcedony is as gem material, and many gem names are applied to variously colored or patterned chalcedony. When banded, it is called agate, when red or yellow and opaque it is called jasper, when translucent green it is chrysoprase, and when translucent orange it is carnelian. Flint is dark gray or brown chalcedony.

California Counties in Which this Mineral is Found
 

Alameda
Alpine
Amador
Butte
Calaveras
Colusa
Contra Costa
Del Norte
El Dorado
Fresno
Glenn
Humboldt
Imperial
Inyo
Kern
Kings
Lake
Lassen
Los Angeles
Madera
Marin
Mariposa
Mendocino
Merced
Modoc
Mono
Monterey
Napa
Nevada
Orange
Placer
Plumas
Riverside
Sacramento
San Benito
San Bernardino
San Diego
San Francisco
San Joaquin
San Luis Obispo
San Mateo
Santa Barbara
Santa Clara
Santa Cruz
Shasta
Sierra
Siskiyou
Solano
Sonoma
Stanislaus
Sutter
Tehama
Trinity
Tulare
Tuolumne
Ventura
Yolo
Yuba
 
 

Information on Specimen Photo:
Specimen Description: Chalcedony is a quartz variety. This specimen exhibits a reniform habit, meaning kidney shape, and is from the Mojave Desert in California.
Photographer: Dale Stickney, CGS.