Akadama - Akadama

This refers to reddish-brown jasper that is used for garden stones, water stones, decorative stones, etc. Its reddish-brown color is due to the hematite it contains. It is almost opaque. Its hardness is almost equal to that of quartz, and it develops a beautiful luster when polished. It is found in iron deposits with rocks rich in silica as their host rock, or in the silicified zones of iron-containing deposits. It is also often found as veins in acidic volcanic rocks. The jasper found in Akadama, Sado City, Niigata Prefecture, and its surrounding areas is famous.

[Satoshi Matsubara]

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

赤褐色をした碧玉(へきぎょく)で、庭石、水石、飾り石などに使われるものをいう。赤鉄鉱を含んでいるため赤褐色にみえる。ほとんど不透明。硬度は石英にほぼ等しく、研磨すると美しい光沢が生ずる。ケイ酸分に富む岩石を母岩とする鉄鉱床、あるいは鉄を含む鉱床の珪化(けいか)帯に産する。また酸性火山岩中の脈としてもよくみられる。新潟県佐渡(さど)市赤玉およびその付近から産するものが有名。

［松原　聰］

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