Elvan is a name given locally to the quartz-porphyries which occur as dikes in Cornwall; in many of them the matrix contains scales of colorless muscovite or minute needles of blue tourmaline.
In many of them the matrix contains scales of colorless muscovite or minute needles of blue tourmaline. Elvan is a name given locally to the quartz-porphyries that occur as dikes in Cornwall.
Elvan is a name given locally to the quartz-porphyries that occur as dikes in Cornwall. In many of them the matrix contains scales of colorless muscovite or minute needles of blue tourmaline.
Elvan is a name given locally to the quartz-porphyries that occur as dikes in Cornwall. In many of them the matrix contains scales of colorless muscovite or minute needles of blue tourmaline.