We have recently started igneous rocks and have been exploring classification, based on texture and composition. The birth of extrusive rocks, such as basalt under water is spectacular.
The link below shows some footage filmed underwater on a lava dive near Hawaii. A classic piece starts at about 1:18.
Pillows Filmed Near Hawaii
Living in Newfoundland, many are surprised at the wide range of igneous rocks we have here. Granite and gabbro are quite common and well exposed. The potentially cooler aspect is that we have lots of volcanics too. Rhyolite and basalt also provide evidence of our volcanic past. We see some rhyolites in the western section of the Avalon zone, but it is in the central region (the Dunnage Zone) where ocean-ocean plate collision during the closing of the Iapetus Ocean gave rise to submarine volcanism.
The result is an abundance of pillow lavas which are now exposed in the central areas of the province, especially around the shorelines near the town of Springdale.
They look remarkably like those seen below, in a photo from Brittany, France.
Pillows most often appear in the rock record as above - a stack or mound like structure with individual pillows laying atop one another. Shapes are generally oval.
Given that many have escaping gas, vesicles are found mainly near the top. Likewise, they are convex on their top surface (probably due to bending over other pillows below). These guidelines, among others, are quite useful in determining the top and bottom of a sequence....pretty cool.
