Noun
A hard, earthy ore of iron.
Source: Webster's dictionaryAn opal doublet consists of a relatively thin layer of precious opal, backed by a layer of dark-colored material, most commonly ironstone, dark or black common opal (potch), onyx, or obsidian. Source: Internet
It is unclear whether these banded ironstone formations were seasonal, followed some feedback oscillation in the ocean's complex system or followed some other cycle. Source: Internet
Origins An ashtray carved out of a soft form of banded ironstone from the 3.5 billion year old Barbeton Supergroup in South Africa. Source: Internet
The first two are blue fibrous minerals, with glaucophane occurring in blueschists and crocidolite (blue asbestos) in ironstone formations, both resulting from dynamo-metamorphic processes. Source: Internet
When the building burned before this present 1914 William Cass Aldrich structure was built, the children went for a few years to classes in the nearby Ironstone mill which is now demolished. Source: Internet