**This EC cannot be completed at night. Ruler/measuring device needed. No group responses accepted. A specific photo at GZ is required as part of the log**
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. 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. It is specifically a type of monzonite notable for containing thumbnail-sized crystals of feldspar. These feldspars are known as ternary because they contain significant components of all three endmember feldspars. The feldspar has partly unmixed on the micro-scale to form a perthite, and the presence of the alternating (alkali) feldspar and plagioclase layers give its characteristic silver-blue schiller effect (called labradorescence) on polished surfaces and when looking from different angles. Olivine, apatite and quartz can also be present. Larvikite is usually rich in titanium, with titanaugite and /or titanomagnetite present.
Larvikite occurs in the Larvik Batholith (also called the Larvik Plutonic Complex), a suite of ten igneous plutons emplaced in the Oslo Rift (Oslo Graben) surrounded by ~1.1 billion year old Sveconorwegian gneisses. The Larvik Batholith is of Permian age, about 292–298 million years old, in association with the break-up of the super continent of Pangea. Larvikite is also found in the Killala Lake Alkalic Rock Complex near Thunder Bay (Ontario).
The name originates from the town of Larvik in Norway.
Source: Wikipedia
Schiller Effect
Schiller (German, literally "shimmer"), is the metallic iridescence originating from below the surface of a stone that occurs when light is reflected between layers of minerals. It is seen in moonstone and labradorite and is very similar to adularescence and aventurescence.
***
At GZ and extending along the Bay St frontage you will see examples of larvikite. In order to complete this EC, please submit your answers to the following questions via the in-game messaging system, and post the required photo with your log. Group answers are not accepted. I read and reply to all responses; smilies claimed without the required answers & photo will be deleted without further notice.
***
Questions:
1. Describe the larvikite that you can find on this building. What colours can you see? How are the crystals arranged?
2. Why do you think the crystals are the size they are?
3. Now look at the brightest crystals. What is their average size (in mm/cm)? Can you see any patterns in them (re: shape, organization)?
4. Describe in your own words why the crystals display this iridescent optical effect.
5. Name 2 other rocks that exhibit the schiller effect.
6. Required photo - post with your log - you/your GPS/your caching name in front of GATE #3 (the gate number MUST be visible in your photo - it is found above the doors to the gate). NO larkivite spoilers, please.
***
Thanks for visiting - I look forward to receiving your answers and viewing your photo of Gate #3. No group responses - everyone must submit their answers & post their own photos.