Geography
There are eight mountains over 400 m high, the tallest mountain is Mt. Hongtoushan (紅頭山) at 552 m. The rock on the island is volcanic tholeiite andesite, and volcanic explosive fragments. The volcano erupted in Miocene to Miocene period. It is part of the Luzon Volcanic Arc. Magma was formed from underthrusting oceanic crust under compression about 20 km deep. The andesite rock contains some visible crystals of pyroxene or amphibole. The geochemistry of the rock shows it is enriched in sodium, magnesium and nickel, but depleted in iron aluminium, potassium titanium and strontium.
Read more about this topic: Orchid Island
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