![]() However, some agates do not have obvious bands. If you hold it up to the light and pass your hand between the material and the source of light, your hand will block the light passing through the material.Īgate is generally a banded material, and observing bands in a specimen of chalcedony is a very good clue that you have an agate. If you hold a translucent piece up to a source of light, you will see a small amount of light passing through the thin edges. If you have a piece that is semitransparent, you will be able to hold a very thin piece up to the light and see distorted or foggy images through it. With its colorful appearance, ability to accept a bright polish, durability to survive the tumbler, ready availability, and low price, chalcedony is the perfect material for making tumbled stones.Īgate is a translucent to semitransparent chalcedony. It can also be banded or have plume, dendritic, mottled, mossy or other colorful structures within. It is commonly gray, white, brown, red, yellow, orange and black, but it can occur in any color. Now you know how to tell chalcedony from other types of quartz.Ĭhalcedony occurs in a wide range of colors. Thus, much of the light that strikes chalcedony fracture surfaces is scattered instead of reflected, hence the dull or waxy luster. A disturbance occurs at each crystal boundary, which causes slight irregularities on the curved fracture surfaces. When it fractures, the fracture surface must propagate across thousands of quartz microcrystals. This luster difference is caused by the microcrystalline nature of chalcedony. Some people find that dull to waxy luster surprising because broken pieces of quartz have a bright, vitreous luster. These freshly broken pieces of chalcedony have a dull to waxy luster. Chalcedony has a hardness of approximately 7 on the Mohs hardness scale.Ĭhalcedony breaks with a conchoidal fracture, meaning its broken pieces often have smooth, curved surfaces. That's why ancient people sought out chalcedony for making their tools and weapons (it was often called "flint"). Other types of quartz have much larger crystals - often many inches or feet across.Ĭhalcedony is a very hard and very durable material. "Microcrystalline" means that the quartz is in the form of crystals that are so small that a microscope must be used to visualize them individually. "Quartz" is the name of a mineral composed of silicon and oxygen (SiO 2). ![]() Agate and jasper are both varieties of chalcedony. Chalcedony is a generic name given to materials that are composed of microcrystalline quartz. ![]()
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