This Earthcache

At the end of January 2023 I was up in Dublin on a daytrip to deliver some resident assessments. After a sinfully large breakfast nearby, I was walking along Thomas Street and the sun was just at that perfect angle to spot one of my favourite cladding stones, larvikite. Although I have long promised myself not to pepper Dublin with a ton of low effort generic building earthcaches - both for sanity and effort reasons - this one I just couldn't resist as it's quite rare to see here.
 

This earthcache is best done during the day with the sun out, as the rock looks the best. If you do choose to do it at night, just beware this isn't the best part of town.

Larvikite

Larvikite is an intrusive igneous rock, i.e. it was formed during the slow cooling process of magma deep (about 30 kms) below the earth's surface. This occurred in the early Permian time, about 298-293 million years ago, in association with the break-up of the super continent Pangea and eventual formation of the Oslo Rift. Larvikite is comprised nearly entirely of feldspar, but can also contain small amounts of other minerals. Larvikite comes in several varieties which differ slightly in colour and composition. 

After its formation deep below ground the Larvikite was slowly transported to the surface by a variety of geological processes. The conditions on the surface led to microscopic changes within the feldspar crystals. They have a microstructure which creates the colours that you can see when looking at the stone from different angles. This optical effect is known as Schiller effect or labradorescence (Labradorite is another feldspar mineral that shows this effect very impressively).

Larvikite is highly valued as a dimension stone, i.e. natural stone that is cut and finished to specified sizes and shapes, which can be used for buildings, monuments, paving, furniture, and decorative objects. As a very durable material Larvikite is mostly used for facades on commercial buildings, but also for kitchen worktops, bar counters and gravestones. 

You'll see it here at the building on the north side of the road at GZ - a dark rock near ground level that looks like it has white pieces in it. But if you walk past it you'll see it shimmering and changing colour.

Questions

Answer the following questions and send them to me via the Messenger or via an email. Feel free to log the cache before you send them, but please send them within a reasonable timeframe. Sending no answers may result in your log being deleted, with fair warning. Optional questions are just that, optional, they are for the earthcache nuts (like me) who enjoy looking that bit more closely.

At the given co-ordinates you'll see a black polished rock just above ground level at the side of the building.

1. What rock do you see here? Describe it, and the colours you observe when standing looking at it.
2. Move along the front of the building and tell me what colours you see in the larvikite and whether these appear to change as you walk.
3. Look at the brightest crystals. What is their average size? Can you see any patterns in them?
4. Describe in your own words why the crystals display this iridescent optical effect.
5. Optional: Describe the physics of the Schiller effect to me in detail.
6. Optional: What other minerals are present in larvikite?