#cool rocks

Had it out at the park and found two amazing rocks.

Petrified wood and a grey druzy agate.

Today’s Specimen: Gneiss

‘That’s a gneiss rock!’ Is always everyone’s favourite thing to say. I know, it’s mine too. But what exactly are we looking at?

Gneiss is a foliated metamorphic rock (composed of thin layers) composed of felsic (lighter bands) and mafic (darker bands) minerals, and unlike some other foliated rocks, it does not usually split along the layers. Gneiss usually feels rough, and falls between a 6 and 7 on the Mohs scale, making it useful for construction purposes. Gneiss is an extremely common rock to find in mountainous regions, and other areas with ancient continental crust worldwide. (Check out the Acasta Gneiss in Canada, which is the oldest known intact rock formation in the world!)

Today’s Specimen: Travertine

A type of limestone, travertine is formed by precipitation of several minerals, but is primarily calcite. Travertine is created from the buildup of calcium carbonate coming out of groundwater, which begins to form gradual layers of stone. This rock will usually be found near wet areas, such as caves or springs. This rock is ranked between a 3 and 5 on the Mohs scale. Due to travertine being a desirable building material, extraction is a very particular process. Small, aligned holes are drilled into the rock to allow for explosives to be placed. The strategically placed explosions allow for easy removal, which can then be further processed. Travertine is used for a diverse variety of purposes as a building material, including: Exterior facades (the Roman Colosseum was made from travertine in 72 CE, and it still stands today!), backsplash, flooring, paving, and countertops. Travertine can be found in many places, with major quarries in: Italy, Iran, Türkiye, Peru, Mexico, and the USA. There are many different varieties and finishes of travertine, each can be utilized in different ways.

Stay tuned for another Rock Talk!