Walking past GZ I could instantly recognise these rocks. Living near the region of these gemstones I knew I had to write up an EC about it.

Answers can be short and precise. I have tried to include as much information as possible in the listing, and I'll be honest, metamorphism is such a broad topic... If I added any more information it would be a chemistry class. In any case, enjoy the greenery.

Observe the greenish panels

1. Looking at the marble, do you think this is a calcium carbonate or calcium manganate marble? Why?
2. Is it pure? Give reasons.
3.  Do you think this marble has been through regional or contact metamophism? Why?
4. Given the text below, what P/T do you think metamorphised the rock?
5. Do you think the marble has undergone metasomatism? Were minerals introduced or removed, and which mineral? What is the name of the new mineral?
6. What % of the marble has been serpentinized?

Metamorphism

Metamorphic rocks are rocks that have undergone alteration through heat and pressure. Some examples with explanations:

1. Pure sandstone, which is silicon dioxide, recrystallises into quartz, also silicon dioxide.
2. Pure limestone, which is mostly calcium carbonate, recrystallises into calcite, also calcium carbonate.
3. The most famous of them all, carbon, under extreme heat and pressure, becomes diamond.

As you can see, metamorphosis alters the original rock (protolith) into a new rock, with the same elements just arranged in a different structure.

Regional Metamorphism vs Contact Metamorphism

Contact metamorphism occurs when molten rock contacts a protolith. Upon contact, the protolith heats up, melts and recrystallises. This usually means that the pressure is much lower and a smaller area affected.

Regional metamorphism takes places on a wider scale during geologic events such as mountain building. This usually indicates higher temperature and pressures.

How do we know? Here's a diagram:

Metamorphic Grades

As mentioned metamorphism involves heat and pressure. And depending on the protolith as well as the heat and pressure, certain minerals form. These are what is called metamorphic facies.

TL;DR - I found mineral X,Y,Z in rock A. Therefore rock A must have metamorphosed under conditions that can form minerals X Y Z.

Ooh a chart! Honestly I can't be bothered to explain, but here are some answers for the questions: 

Diopside, forsterite, tremolite formed during metamorphism are part of the amphibolite facies. All 3 minerals have magnesium, silicon and calcium. Wink wink.

Metasomatism

Metasomatism, unlike metamorphism, actually changes the chemical composition of the rocks. Also called hydrothermal alteration, this happens when geothermally heated water introduces or extracts chemicals as it migrates through the original rock.

From my understanding, serpentinization is a form of metasomatism. Serpentine has the chemical composition of Mg₃Si₂O₅(OH)₄ (Something seems missing here..)

Connemara Marble

Regarded as the national stone of Ireland, this stone begins its life as an impure dolomitic limestone (CaMgCO3)2) with Silicon (Si) impurities. It then undergoes metamorphism, in this case minerals formed include diopside, forsterite, tremolite, together with talc and chlorite. Serpentinization altered these minerals into serpetine subgroup minerals. The leftover minerals formed schist and quartzites.