Basalt Columns at the Mt Tomar Botanic Gardens

One of the reasons Mt Tomar supports such lush vegetation is that it’s soil derives from the basalt which caps the mountain. Basalt is a very fine grained, dark coloured rock of volcanic origin. It’s abundant in iron, magnesium, calcium and other elements and weathers to form a mineral rich soil that plants love.

I was hoping to see some of the basalt flows but the weather was pretty miserable so we didn’t spend as much time as I would have liked looking about. I did notice the garden walls just below the visitors center were made from presumably local basalt columns. A closer look at the rocks revealed olivene phenocrysts and small vesicles some of which were lined with white crystals, possibly calcite or aragonite?

The walls looked good, and it’s pretty amazing to think that a few million years ago they were part of a massive lava flow!

Columnar Basalt retaining wall at the Mt Tomar Botanic Garden. See Will for scale.

• Basalt
• Volcanic