About Boulder rock:
Boulder Rock, located in Midgegooroo National Park, is a spectacular large granite rock formation with several large boulders. boulder rock is also a great popular picnic spot.
Boulder Rock Indiginous History:
Boulder rock at Midgegoroo National Park holds significance for local Aboriginal people, with the area's name meaning "place of the gum blossom" and "top of a hill" in the local Wadjak language.
What is granite:
Granite is a coarse-grained intrusive igneous rock composed mostly of quartz, alkali feldspar, and plagioclase. It forms from magma with a high content of silica and alkali metal oxides that slowly cools and solidifies underground. Lava forms granite when it cools deep below the surface, and then it cools very slowly, allowing crystals to form much larger than when lava cools at the surface in the area.
How is granite formed in steps:
- Magma Generation: Magma forms from melted continental crust, often near tectonic plate boundaries or during continental collisions, where heat and pressure melt rock.
- Slow Ascent: This thick, silica-rich magma slowly rises through the Earth's crust, like a giant balloon, forming large underground chambers called plutons.
- Deep, Slow Cooling: Trapped deep within the crust, the magma cools over thousands to millions of years, allowing minerals to form large, interlocking crystals.
- Crystallization: As it cools, minerals like quartz (grey/glassy), feldspar (pink/white), and mica (shiny black/silver) solidify from the molten rock.
- Exposure: Over vast geological time, erosion and uplift wear away the overlying rock layers, eventually exposing the granite formations at the surface.
Weathering at Boulder rock:
The weathering that can be found at Bulder rock is spheroidal weathering. spheroidal weathering is a type of chemical weathering where concentric, onion-like shells of decomposed rock peel off a central corestone, creating rounded boulders. It happens in jointed bedrock (like granite) as water penetrates fractures, attacking corners and edges first, causing chemical changes (like feldspar turning to clay) that expand and weaken the rock, leading to rounded forms, it can also be called onion-skin or woolsack weathering.
sources:
Experience Perth hills
How to obtain the Cache find:
In order to log this cache you will have to send me a private message either by email or GC Messenger with the answers to the cache , if you have not sent me a message with answers in 10-14 days your log will be deleted.
1. What type of weathering can you find at this rock?
2. What are the steps in creating Granite?
3. What do you think is in Granite?
4. Is Granite formed when lava cools down or is heating up
Take a photo of yourself or an personal object that clearly shows your geocaching name showing the Rock the photo must be uploaded with the log.
congratulations to Murazor and Lady Murazor for FTF 😎