Alice Springs has rocks everywhere and if you’re observant you’ll see many different types of rock as you geocache around town. There is a Joint Geological/Geophysical Reserve located adjacent to the Historic Telegraph Station Reserve that has numerous walking and mountain biking trails which take you past various rock features.
This earth cache requires a round trip walk of around 5km along the Simpson Gap Track during which you will visit and identify three types of rock. The rock types you’ll be identifying can be found at the given way points, all you need to do is tell me which rock type described below is located at each waypoint.
Basalt
Basalt is a mafic (rich in iron and magnesium and therefore generally darker in colour) extrusive rock (refers to the mode of igneous volcanic rock formation in which hot magma from inside the Earth flows out (extrudes) onto the surface as lava), it is the most widespread of all igneous rocks and comprises more than 90% of all volcanic rocks. Generally, basalt is fine grained due to the rapid cooling giving little time for the growth of crystals.
Conglomerate
Conglomerate can have a variety of compositions. As a clastic sedimentary rock, it can contain clasts* of any rock material or weathering product that is washed downstream or down current. The rounded clasts of conglomerate can be mineral particles such as quartz or feldspar, or they can be sedimentary, metamorphic, or igneous rock fragments. Clasts of quartzite, sandstone, limestone, granite, basalt, and gneiss are especially common. The matrix that binds the clasts together can be a mixture of sand, mud, and chemical cement. Common chemical cements are calcite or quartz.
*A clast is a fragment of geological detritus, chunks and smaller grains of rock broken off other rocks by physical weathering
Quartz
Quartz is one of the most well-known minerals on earth. It occurs in basically all mineral environments, and is the important constituent of many rocks. Quartz is also the most varied of all minerals, occurring in all different forms, habits, and colors. There are more variety names given to Quartz than any other mineral. Pure quartz is clear. Color variance due to impurities: purple (amethyst), white (milky quartz), black (smoky quartz), pink (rose quartz) and yellow or orange (citrine). Milky quartz, snow quartz or white quartz is the most common variety of crystalline quartz. The white color is caused by minute fluid inclusions of gas, liquid, or both, trapped during crystal formation. White quartz may be stained or streaked with mineral contamination.
To claim this earth cache email or message me saying which rock type was at:
WP1
WP2
WP3
It is not necessary to wait for my reply before logging your find but not providing answers or providing the wrong answers may result in your log being deleted.
Safety note: there are no facilities at the suggested parking location (Flynn’s Grave Carpark) and along the Simpson Gap trail. Come prepared, particularly in summer, with a hat, sunblock and plenty of water. The Simpson Gap Trail is sealed and therefore an easy walk. However, you will need to leave the sealed trail to visit several waypoints.
Sources
https://geology.com/rocks/basalt.shtml
https://www.minerals.net/mineral/quartz.aspx
https://mineralseducationcoalition.org/minerals-database/quartz/
https://flexiblelearning.auckland.ac.nz/rocks_minerals/rocks/conglomerate.html