Não informado. (2000). United Kingdom mineral statistics. British Geological Survey.
Chicago (17e ed.) BronvermeldingNão informado. United Kingdom Mineral Statistics. London: British Geological Survey, 2000.
MLA (8e ed.) BronvermeldingNão informado. United Kingdom Mineral Statistics. British Geological Survey, 2000.
Let op: Deze citaties zijn niet altijd 100% accuraat.