Koroit opal ct.20.37

Boulder opal: Koroit This type of boulder is formed in the same way as the classic one: a silica solution filled the fractures or cavities of a sandstone rich in iron ( ironstone),either dissolves other mineral that was originally in those spaces. Sometimes the spaces can be very small but in large areas with intricate nice patterns throughout the nodule, which could result in Koroit or Yowah-nut type opal.From Queensland, Australia. Size:334.2x17.2x6.2 mm Weight: 20.37 ct. CODE# 2297