7.6" Polished Brazilian Agate Slice
Agate has also been known to fill veins or cracks in volcanic rock. Such agates, when cut transversely, exhibit a succession of parallel line giving a banded appearance to the section. Such stones are known as banded agate, riband agate and striped agate.
The agates from Brazil are mined from decomposed volcanic ash and basalt from the late Permian age (248-275 million years old) In Rio Grande do Sul the "agate mines" are normally just plowed fields in which loose agates are found and collected. These agates can be very colorful and polish beautifully.