Question

1. how does serpentinite form? I.e. what type of metamorphism?
2. What is one MAIN way to distinguish quartzite from marble since they often look similar? Think about the physical properties you used to test minerals.

Answer 1

During the Retrograde metamorphism when an ultramafic igneous rock undergoes loss of heat it gradually loss it's temperature and the olivine crystal present in it is altered to serpentine. Olivine generally form at very high temperature approximately at about 1890oC but by gradual fractionation and partial melting it is no longer stable and got altered to the serpentine. This Retrograde metamorphism is an event of Regional Metamorphism when Magma just emplaced from the depth of mantle. So serpentinite is a very Low grade Ultramafic Metamorphic Rock. Due to the alteration of olivine the particular metamorphic rock shows a typical Mesh texture or Symplectite texture which is a reaction rim or Corona forming texture. Bastite is a typical term that represent the fibrous Serpentine form through this process.

If we look out the physical properties of the rock Quartzite and Marble than we can make differences in there hardness because the rock Quartzite consists of Abundance Quartz having a hardness of 6 but Marble consists of Carbonate or calcite having a hardness of about 3.

We can also go throught the acid testing of both the rock and marbMawill give positive response as it will reacts with Acid and will give rise to the CO2 gas , whereas the Quartzite will non reactive to the acid .

Careful observation of marble can came ip with rhomohedrrho cleavages but quarziteQ is lack of cleavage.