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Chalcedony

Crystal system · Trigonal

Chalcedony is a tectosilicate mineral prized by collectors for its exceptional color range, with several world-class Chinese localities.

Front view of botryoidal grape agate cluster from Sulawesi

About Chalcedonyextended article

IMA Abbreviation (Whitney-Evans 2010)
Cha
→ Chalcedony
Cryptocrystalline quartz
Standard symbol from American Mineralogist (Whitney & Evans, 2010). Used in thin-section labeling, phase diagrams, and IMA-style species records.
Pronunciation
/kælˈsɛdəni/
↔ kal-SED-uh-nee
four syllables (Greek)
UV Fluorescence
SW (254 nm)
Green
weak
LW (365 nm)
Green
weak
U-activated examples; locality-dependent.
SW = shortwave (germicidal lamp). LW = longwave (blacklight). Response varies with locality, trace impurities, and treatment.
Diaphaneity (Transparency)
translucent
Cryptocrystalline; light passes through edges only.
Specific Gravity
2.58–2.64
g/cm³
light
Cryptocrystalline quartz; slightly lower SG.
For comparison: water = 1.00, glass ≈ 2.5, quartz = 2.65, corundum ≈ 4.00, galena ≈ 7.50, gold ≈ 19.3.
Market availability: Common
Widely available in most dealer stocks. Specimens span all price tiers.
Collector tier: Solid Display
Reliable mid-tier display species. Easy to find in well-formed examples; broad locality diversity.
Mohs 7
Vickers (~) 1400 HV
Knoop (~) 1100 HK
Geological setting
Volcanic
Element composition by mass

Formula: SiO₂ (cryptocrystalline) · molar mass: 60.08 g/mol

O 53.26%
Si 46.74%

Computed from atomic weights (IUPAC 2021). Site-occupancy groups (Fe,Mn) split equally.

GroupQuartz Group (silica)
Related members: Quartz · Amethyst · Citrine · Rose Quartz · Agate · Jasper
Mohs Hardness 7

Chalcedony sits at 7 on the Mohs scale — harder than glass; scratches steel.

Colors:
Streak
White
Crystal system
Trigonal (microcrystalline)
Oxides & HydroxidesOxides (Silica Group)
TL;DR · 1 min read
Chalcedony is the cryptocrystalline form of quartz — submicroscopic interlocked quartz fibers producing a tough, waxy-lustered material. Many named varieties are Chalcedony: agate (banded), carnelian (red-orange), chrysoprase (apple-green Ni), bloodstone (green with red jasper), and onyx (parallel-banded).

Chalcedony is the cryptocrystalline form of quartz — submicroscopic interlocked quartz fibers producing a tough, waxy-lustered material. Many named varieties are Chalcedony: agate (banded), carnelian (red-orange), chrysoprase (apple-green Ni), bloodstone (green with red jasper), and onyx (parallel-banded). Chalcedony forms in basalt cavities and silica-replacement environments.

More minerals to explore

Varieties of Chalcedony

Chalcedony is a parent species — the following named varieties differ in color or chemistry but share the same fundamental mineralogy.

  • Onyx (u7f1fu739bu7459)
    parallel banded black-and-white
    Black-and-white parallel-banded chalcedony variety, used for cameos.
  • Sardonyx (u7ea2u7f1fu739bu7459)
    red-and-white banded
    Red-and-white parallel-banded chalcedony, used for cameos and intaglios.
  • Carnelian (u7ea2u7389u9ad3)
    red-orange
    Iron-bearing reddish-orange chalcedony variety.
  • Sard (u6df1u8910u7389u9ad3)
    brownish-red
    Darker-brown carnelian-related chalcedony variety.
  • Chrysoprase (u7effu7389u9ad3)
    apple-green
    Nickel-bearing apple-green chalcedony variety; the rarest chalcedony color.
  • Bloodstone (Heliotrope) (u8840u77f3)
    green with red spots
    Dark-green chalcedony with red iron-oxide spots resembling blood drops.

About Chalcedony

Chalcedony is a tectosilicate mineral in the quartz group and has the chemical formula SiO2. It crystallizes in the trigonal system and is one of the most visually varied minerals in the collector market. Its combination of structural character and global distribution make it a recognized species in both systematic and aesthetic collections.

Identification & care

Chalcedony typically forms microcrystalline to cryptocrystalline masses; nodules, botryoidal coatings, stalactitic; no visible crystals. Its color range is broad, including white, gray, blue, pale blue (classic), and also many other colors. The luster is waxy to dull, the streak is white, and specimens are typically translucent. The fracture is conchoidal, which is one of its key identifying features.

Collector context

How it forms

Chalcedony forms in low-temperature hydrothermal; volcanic vesicles; replacement of limestone; weathering; diagenetic in sediments. It is commonly found in association with quartz, calcite, zeolites, opal.

Classic Chinese localities

Documented Chinese occurrences are recorded at Shangbao Mine, Jiama Cu-polymetallic deposit and Jinduicheng Mine, among others.

Why collectors care

Collectors pursue Chalcedony for its patterns, color depth, and polish response rather than for pattern character. Good material has a surface that polishes cleanly, a visual character that holds up in direct light, and enough size to anchor a display on its own. Chinese sources, where present, supply much of the material currently cut and sold as decorative pieces.

What affects value

Value in Chalcedony is assessed, in typical order of weight, against: (1) source locality; (2) size; (3) pattern and visual character; (4) color depth and distribution; (5) polish response and surface finish; (6) piece integrity (absence of major cracks or chips). Uniqueness of pattern and verified source region add significantly to decorative pieces.

Naming history

The name Chalcedony has a specific etymological and historical context — see Mindat's reference entry for provenance details. We have retained naming data at the record level; published prose is paraphrased from factual fields rather than copied from source.

Available Chalcedony specimens

1 specimen
Front view of botryoidal grape agate cluster from Sulawesi
Indonesia

Grape Agate Cluster – Botryoidal Chalcedony – Sulawesi, Indonesia

$86.36

Recently sold Chalcedony specimens

2 examples — for reference
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Front view of vivid purple grape agate from Mamuju

Grape Agate Chalcedony – Vivid Purple Botryoidal – Mamuju, Sulawesi

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Front view of purple botryoidal grape agate from Indonesia
Indonesia

Grape Agate Chalcedony Cluster – Purple Botryoidal – Indonesia

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