Partridge Island (Nova Scotia) - Geology and Gems

Geology and Gems

Partridge Island stands at the edge of the ancient rift valley known as the Fundy Basin that was created when the supercontinent Pangaea began to break up about 225 million years ago. As the continental plates moved apart, they ruptured, and blocks subsided along fault lines forming the rift valleys that became sedimentary basins. The Fundy Basin is the largest of these basins in Eastern North America. During the Triassic geological period between 208 and 220 million years ago, rivers swollen by intense rains carried coarse sediments (now sedimentary rocks) from nearby highlands into the Fundy Basin. Other deposits came from wind-blown sand dunes. Later, large lakes formed on the central part of the basin depositing finer sediments up to 1,000 metres thick and, as they dried up periodically, they left behind salt and gypsum deposits.

The red sedimentary sandstone base of Partridge Island dates from the late Triassic period. The covering layer of dark basalt was formed from magma and lava eruptions in the Jurassic period between 175 and 208 million years ago as continental drifting further weakened the earth's crust. Sandstones and siltstones were deposited on top of the basalt during cycles of drought and rain. Although sandstone is soft and easily eroded, it forms high, steep cliffs where it is covered by basalt. The basalt cliffs of Partridge Island contain small cavities formed when gases escaped as the lava cooled. Water seeping through these cavities or vesicles deposited minerals including gemstones such as amethyst, agate, jasper and calcite. Zeolite minerals such as chabazite and stilbite can also be found at Partridge Island.