DigMyGem Gem encyclopedia

Bicolor Agate

Chalcedony & Agate Family

Bicolor agate is a descriptive name for agate whose natural chalcedony bands or zones show two dominant contrasting colors. It is not a separate mineral variety: agate is fibrous, microcrystalline quartz characterized by repeated bands, commonly deposited inside rock cavities.

Identity

Material or variety
Agate
Scientific or material identity
Agate (banded chalcedony)
Classification
Natural mineral or mineral variety
Composition or formula
SiO₂
Crystal system or structure
Aggregate or composite structure
Geological or manufacturing origin
Forms from silica- or mineral-rich fluids in cavities and fractures.
Mohs hardness
6.5 to 7
Specific gravity
2.58 to 2.64

Origins

Brazil · Mexico · USA

Appearance & optical properties

agate with two strongly contrasting warm and cool color zones.

History & discovery

The name agate traces to the Achates River in Sicily, where the Greek naturalist Theophrastus described the stone. People have used agate for tools and ornaments since prehistory, and ancient Mediterranean craftspeople cut it for beads, jewelry and engraved seal stones.

Uses & care

Common uses
Strong color boundaries are displayed in sliced nodules, cabochons, beads and carvings. Agate has also served historically for seals, mortars, balance bearings and other objects needing a hard, polishable surface.
Handling and cleaning
Clean it with warm soapy water and a soft brush or cloth. Protect it from sharp impacts and sudden temperature changes; avoid harsh chemicals and prolonged strong light when the origin or stability of its colors is uncertain.

Jewellery

13 pieces of Bicolor Agate jewellery. Learners earn each one in DigMyGem by learning words; until then it shows as a silhouette.

  • Silhouette of Tazza Farnese

    Tazza Farnese

    Jewel

    A large Hellenistic cameo bowl carved from a single banded sardonyx, once owned by the Medici and now in Naples.

    Photograph of Tazza Farnese
    Photo: Ana al'ain, Public domain, via Wikimedia Commons
  • Silhouette of Gemma Augustea

    Gemma Augustea

    Jewel

    A Roman sardonyx cameo of about AD 10 showing Emperor Augustus enthroned, now kept in Vienna.

    Photograph of Gemma Augustea
    Photo: Dioscurides (?), CC BY-SA 3.0, via Wikimedia Commons
  • Silhouette of Great Cameo of France

    Great Cameo of France

    Jewel

    A three-layer sardonyx cameo of the first century AD, the largest ancient cameo to survive, held in Paris.

    Photograph of Great Cameo of France
    Photo: Bibliothèque nationale de France, Public domain, via Wikimedia Commons
  • Silhouette of Gemma Claudia

    Gemma Claudia

    Jewel

    A five-layered Roman sardonyx cameo made about AD 49 showing Claudius and Agrippina the Younger facing Germanicus and Agrippina the Elder, now in the Kunsthistorisches Museum, Vienna.

  • Silhouette of Rubens Vase

    Rubens Vase

    Jewel

    A Late Antique Byzantine vase carved from a single piece of honey-coloured agate and named after the painter Peter Paul Rubens, who once owned it; it is now in the Walters Art Museum.

    Photograph of Rubens Vase
    Photo: Anonymous ( Byzantine Empire ) Unknown author, Public domain, via Wikimedia Commons
  • Silhouette of Pylos Combat Agate

    Pylos Combat Agate

    Jewel

    A Minoan agate sealstone carved about 1450 BCE with three fighting warriors, found in 2015 in the Griffin Warrior Tomb at Pylos and called the finest work of Aegean Bronze Age glyptic art.

    Photograph of Pylos Combat Agate
    Photo: Jengod, CC BY-SA 4.0, via Wikimedia Commons
  • Silhouette of Cameo with Valerian and Shapur I

    Cameo with Valerian and Shapur I

    Jewel

    A sardonyx cameo of about AD 260, carved from the stone's coloured layers, showing the Sasanian king Shapur I with a Roman rider; it is kept in the Cabinet des Médailles in Paris.

    Photograph of Cameo with Valerian and Shapur I
    Photo: Marie-Lan Nguyen (4 April 2008), CC BY 2.5, via Wikimedia Commons
  • Silhouette of Marlborough gem

    Marlborough gem

    Jewel

    A large carved onyx cameo showing the wedding of Cupid and Psyche, the most famous gem of the Duke of Marlborough's collection, now in the Museum of Fine Arts, Boston.

    Photograph of Marlborough gem
    Photo: Mark Landon, CC BY 4.0, via Wikimedia Commons
  • Silhouette of Schaffhausen onyx

    Schaffhausen onyx

    Jewel

    An Augustan-era cameo carved in high relief with the goddess Pax Augusta holding a cornucopia and caduceus, given an ornate gold and silver setting in the 13th century and kept in Schaffhausen.

    Photograph of Schaffhausen onyx
    Photo: User:Helvetiker, Public domain, via Wikimedia Commons
  • Silhouette of Vishnu nicolo seal

    Vishnu nicolo seal

    Jewel

    A finely engraved fourth-century agate nicolo seal from Gandhara showing the four-armed god Vishnu with a royal devotee; it has been in the British Museum since 1892.

    Photograph of Vishnu nicolo seal
    Photo: No machine-readable author provided. World Imaging assumed (based on copyright claims)., CC BY-SA 3.0, via Wikimedia Commons
  • Silhouette of Agate Bowl

    Agate Bowl

    Jewel

    The Achatschale is a giant bowl cut from a single block of agate about the fourth century and long treasured by the Habsburgs; it is the largest carved stone bowl in the world, kept in Vienna.

  • Silhouette of Agate Casket of Oviedo

    Agate Casket of Oviedo

    Jewel

    A tenth-century Asturian reliquary box covered in gold sheets set with ninety-nine flat plaques of veined agate, given by King Fruela II to Oviedo Cathedral in 918.

    Photograph of Agate Casket of Oviedo
    Photo: Sitomon, Public domain, via Wikimedia Commons
  • Silhouette of Chalice of Doña Urraca

    Chalice of Doña Urraca

    Jewel

    A jewel-encrusted onyx chalice kept at St. Isidore's Basilica in León, Spain, linked by recent authors to the Holy Grail and once owned by the infanta Urraca of Zamora.

    Photograph of Chalice of Doña Urraca
    Photo: Locutus Borg (José-Manuel Benito Álvarez), CC BY-SA 3.0, via Wikimedia Commons

Sources