Chalcedony in the context of "Petrified wood"

The Środa Treasure (Polish: skarb ze Środy Śląskiej or skarb średzki) is a hoard of silver and gold coinage, gold jewellery, royal regalia and precious stones found in years 1985–1988 during renovation works in the town of Środa Śląska, Poland. The discovered artifacts date from the mid 14th century and comprise over 3,000 pieces. Today it is the property of National Museum in Wrocław and has been kept at the Regional Museum in Środa Śląska.

Vesicular texture is a volcanic rock texture characterized by a rock being pitted with many cavities (known as vesicles) at its surface and inside. This texture is common in aphanitic, or glassy, igneous rocks that have come to the surface of the Earth, a process known as extrusion. As magma rises to the surface the pressure on it decreases. When this happens gasses dissolved in the magma are able to come out of solution, forming gas bubbles (the cavities) inside it. When the magma finally reaches the surface as lava and cools, the rock solidifies around the gas bubbles and traps them inside, preserving them as holes filled with gas called vesicles.

A related texture is amygdaloidal in which the volcanic rock, usually basalt or andesite, has cavities, or vesicles, that are filled with secondary minerals, such as zeolites, calcite, quartz, or chalcedony. Individual cavity fillings are termed amygdules (American usage) or amygdales (British usage). Sometimes these can be sources of semi-precious or precious stones such as diamonds.

The Zvenigorodsky seal, also known as the Persian king and the defeated enemies seal, is an Achaemenid cylinder seal made from chalcedony. It is dated to the late 5 to the early 4 century BCE. In 1930, the Hermitage Museum in Saint Petersburg obtained the seal from a private owner in Kerch (inventory number Гл-501). The seal was first documented in 1881 in Compte rendu de la Commission Impériale Archéologique pour l'Année.

Agate (/ˈæɡɪt/ AG-it) is a variously translucent, banded variety of chalcedony. Agate stones are characterized by alternating bands of different colored chalcedony and may also include visible quartz crystals. They are common in nature and can be found globally in a large number of different varieties. There are some varieties of chalcedony without bands that are commonly called agate (moss agate, fire agate, etc.); however, these are not true agates. Moreover, not every banded chalcedony is an agate; for example, banded chert forms via different processes and is opaque. Agates primarily form as nodules within volcanic rock, but they can also form in veins or silicified fossils. Agate has been popular as a gemstone in jewelry for thousands of years, and today it is also popular as a collector's stone. Some duller agates sold commercially are artificially treated to enhance their color.

Cryptocrystalline is a rock texture made up of such minute crystals that its crystalline nature is only vaguely revealed even microscopically in thin section by transmitted polarized light. Among the sedimentary rocks, chert and flint are cryptocrystalline. Carbonado, a form of diamond, is also cryptocrystalline. Volcanic rocks, especially of the felsic type such as felsites and rhyolites, may have a cryptocrystalline groundmass as distinguished from pure obsidian (felsic) or tachylyte (mafic), which are natural rock glasses. Agate and onyx are examples of cryptocrystalline silica (chalcedony). The quartz crystals in chalcedony are so tiny that they cannot be distinguished with the naked eye.

In geology, silicification is a process in which silica-rich fluids seep into the voids of Earth materials, e.g., rocks, wood, bones, shells, and replace the original materials with silica (SiO₂). Silica is a naturally existing and abundant compound found in organic and inorganic materials, including Earth's crust and mantle. There are a variety of silicification mechanisms. In silicification of wood, silica permeates into and occupies cracks and voids in wood such as vessels and cell walls. The original organic matter is retained throughout the process and will gradually decay through time. In the silicification of carbonates, silica replaces carbonates by the same volume. Replacement is accomplished through the dissolution of original rock minerals and the precipitation of silica. This leads to a removal of original materials out of the system. Depending on the structures and composition of the original rock, silica might replace only specific mineral components of the rock. Silicic acid (H₄SiO₄) in the silica-enriched fluids forms lenticular, nodular, fibrous, or aggregated quartz, opal, or chalcedony that grows within the rock. Silicification happens when rocks or organic materials are in contact with silica-rich surface water, buried under sediments and susceptible to groundwater flow, or buried under volcanic ashes. Silicification is often associated with hydrothermal processes. Temperature for silicification ranges in various conditions: in burial or surface water conditions, temperature for silicification can be around 25°−50°; whereas temperatures for siliceous fluid inclusions can be up to 150°−190°. Silicification could occur during a syn-depositional or a post-depositional stage, commonly along layers marking changes in sedimentation such as unconformities or bedding planes.

Carnelian (also spelled cornelian) is a brownish-red mineral commonly used as a semiprecious stone. Similar to carnelian is sard, which is generally harder and darker; the difference is not rigidly defined, and the two names are often used interchangeably. Both carnelian and sard are varieties of the silica mineral chalcedony colored by impurities of iron oxide. The color can vary greatly, ranging from pale orange to an intense almost-black coloration. Significant localities include Yanacodo, Peru and Ratnapura, Sri Lanka. It has been found in Indonesia, Brazil, India, Iran, Russia (Siberia), and Germany.