Located around the I ❤️ KK Sign are stone sculptures of fish. A closer inspection of the fishes revealed the stone sculptures to be made of Dolerite. This EC aims to help you understand the nature of dolerite and what it is as a rock type.

Igneous Rocks

Igneous Rocks are rocks that are formed when hot, molten rock crystallizes and solidifies. The melt originates deep within the Earth near active plate boundaries or hot spots, then rises toward the surface. These rocks can be further categorised.

Intrusive vs Extrusive 

Intrusive rocks are rocks that cool down and crystallises underground. This results in a slowler and steady cooling process, which causes the crystalline structures of the rock the be larger. These rocks are usually coarse grained, or in geological terms, these rocks are phaneritic.

Extrusive rocks are the opposite, magma flows out and cools above ground, causing the magma the cool and crystallise faster. This causes the crystals to be smaller and fine-grained. In other words, the rock is aphanetic.

Felsic vs Mafic

Felsic is a portmanteau of feldspar and silica, the 2 minerals that are predominant in igneous rocks of this type, with silica being found in the form of quartz. These rocks are generally lighter in colour.

Mafic on the other hand, is a combination of magnesium and ferric, ferric being the latin term for iron (Fe). These rocks are usually darker in colour.

Dolerite

Composition:

1. Plagioclase Feldspar typically consists of a mixture of sodium and calcium aluminum silicates. In diabase, plagioclase feldspar often appears as white to light gray crystals.
2. Pyroxene Minerals (Primarily Augite): Pyroxenes are another group of silicate minerals found in diabase. Augite is the most common pyroxene in diabase. Augite is a dark green to black mineral that contributes to diabase’s overall dark color. It has a monoclinic crystal structure and is rich in iron, magnesium, and calcium.
3. Olivine: Olivine is a green mineral commonly found in mafic rocks. It has a distinctive color and a relatively high magnesium content.
4. Magnetite: Magnetite is a magnetic iron oxide mineral that appears as small black grains in diabase. It contributes to the rock’s magnetic properties.
5. Apatite: Apatite is a phosphate mineral that can be found in small amounts in diabase. It often appears as tiny crystals or grains. In this example it appears of yellow/gold specks.

Questions

Observe the sculptures and answer the following questions

1) Why is dolerite an igneous rock?

2) Is the rock intrusive or extrusive? Why

3) Is the rock felsic or mafic? Why

4) Look closely at the minerals and determine the percentage of the minerals outlined above. 

5) A photolog of the  I ❤️ KK or the sculptures to prove your visit.