One great thing about rocks: you don’t have to mow them. Oh—and you don’t have to water or feed them either. Low maintenance landscaping design? Onto something here? Because brain cells are synapsing away over a few delightful things to ponder. Alright then, it’s on with “Rock the House!”— a purpose revealed if you take the title as a design cue.
Mother Nature, in her wisdom, gives us three types of rocks to reckon with:
- igneous – formed by the cooling process of magma
- sedimentary – formed by weathering cementation or precipitation on the Earth’s surface
- metamorphic – formed by temperature and pressure changes inside the Earth depending on the local environment where they are born and raised.
From any perspective, then, rocks have been through a lot of wear and tear before they become, well, rocks.
Who are these characters?
“Igneous” (sounds like a Roman centurion’s name, but means “ignite”— Latin for fire) a rather ferocious element when it begins its history as molten rock that, as it cools off, becomes more serene when it’s crystalized into minerals. (Wondering about diamonds, now. They are just rocks, after all …turns out they’re metamorphic—formed under pressure. But we could have guessed that when we learned more.) Geologists classify igneous rocks based on both their crystal size and composition, crediting Mother Nature with a prolific variety. Good to know, if we’re going to design with them. Also good to know where they hang out on this continent. Should have guessed the answer to that one without any further information. Where do we find ex-molten lava? Extinct volcanoes–strung out from Cairns through the Glasshouse Mountains in south-eastern Queensland to Mount Napier in Western Victoria. They’re also in the Atherton Tableland through the New England Tableland, and so on, southwards. “Sedimentary” (Latin, meaning “to settle”) rocks take their shape at the Earth’s surface in a couple of ways: “Clastics” (rocks and other materials) become cemented together when chemical precipitation and evaporation can form sedimentary rocks, usually associated with liquid water. Alternatively they can also form in dry, desert environments. The Yarralumla Formation mudstone/siltstone formation is a is a sedimentary formed around 425 million years ago.
Metamorphic rocks are igneous, sedimentary or pre-existing metamorphic rocks that have been changed by great pressures within the crust and upper mantle of the Earth. And–oh, we get it—like a caterpillar transforming into a butterfly, the same rock can change its makeup dramatically over time. Hence—the term metamorph. Yup. We know that one as now we learn that slate can turn into schist, which has visible layers of minerals, which can then turn into gneiss, which shows visible bands of minerals.
Take a test
Most common (back yard) rocks. Can you type them? • Marble • Dolostone • Quartzite • White Chert • Slate • Quartz Knowing rocks by their types is helpful, so now we can take a brief look at their history on this continent.
A Very Brief History
The geology of the Australian Capital Territory includes rocks dating from the Ordovician period—around 480 million years ago—whilst most rocks are from the Silurian period, starting 443 mya, and ending about 417 mya. We get that rocks are old and don’t we wish they could talk? Well, they probably do. We just need to find the station and tune in. A favorite, Uluru, is a large sandstone rock formation… We’ll talk lots about it later, covering all aspects, including design.