War Memorial #2344 ~ Royal Oak Memorial Garden EarthCache

The Royal Oak Memorial Garden is a poignant place. Despite the name, it was established to "offer the chance to reflect on all the lives lost in Scapa Flow in WWI and WWII." As well as the men and boys of HMS Royal Oak. 

There are a number of different elements to the Royal Oak Memorial Garden. Towards its western end is a mounted crest of the Royal Oak. Not far away is a large ship's propeller. Towards the eastern end of the garden is a mounted ship's anchor, near a memorial obelisk that was unveiled on 14 October 2011, on the 72nd anniversary of the sinking of the Royal Oak. The memorial obelisk is made of Granite, a stepped plinth, and a pedestal, with black incised lettering. 

The garden is completed by a display hut in which you find information about the Royal Oak and about the men and boys who lost their lives in her. As well as commemorative wreathes, there are memorials to individual sailors. In some ways the most moving element for us is a display board listing the names and ranks of all those who died. This brings home the sheer scale of the loss of life.

So let us examine and  look closely at the Granite plinth. Granite is an igneous rock made mostly of quartz, feldspar, and mica, plus sometimes other minerals. Each mineral affects the color of the granite based on its chemical composition and light-reflecting properties. Here's a breakdown:

Phenocrysts in granite are large, conspicuous crystals that formed early in the magma’s cooling history and are embedded in a finer-grained groundmass. They stand out due to their size and often distinct color or shape. 

Common Phenocrysts in Granite and Their Identification:

What Causes the Colors in Granite Types?

1. Pink Granite – Rich in potassium feldspar (orthoclase), which is pink.
2. White Granite – Dominated by white plagioclase feldspar and light quartz.
3. Gray Granite – Contains more quartz and sodium-rich feldspar.
4. Black specks – Usually biotite or hornblende.
5. Red or orange tones – Can indicate the presence of iron-rich minerals or altered feldspars.

In granite, the most common phenocrysts are quartz, feldspar (both orthoclase and plagioclase), biotite, muscovite, and sometimes hornblende.

• Quartz phenocrysts appear clear, gray, or smoky. They have an irregular, glassy appearance with no cleavage, a greasy luster, and are hard enough to scratch glass.

• Feldspar crystals, including both orthoclase and plagioclase, are often white, pink, or gray. They tend to be blocky and rectangular in shape. Feldspar shows visible cleavage planes, and plagioclase may show fine striations on its surface.

• Biotite is black to dark brown and forms flaky, platy crystals. It can be identified by its shiny luster and flexible, thin sheets that peel easily.

• Muscovite appears silvery or pale yellow and is also platy like biotite, but lighter in color. It peels into transparent, shiny sheets and is very flexible.

• Hornblende, an amphibole mineral, is dark green to black and has an elongated, prismatic shape. It can be distinguished by its two cleavage directions intersecting at about 60° and 120°, and a splintery, fibrous texture.

The size of phenocrysts in granite provides valuable clues about the cooling history and conditions of formation of the magma:

1. Large phenocrysts indicate slow cooling deep underground. These crystals had time to grow before the rest of the magma solidified. This usually happens early in the crystallization process, when the magma is still mostly liquid and cooling gradually.

2. Smaller or absent phenocrysts suggest faster cooling, where the magma may have cooled more quickly or more uniformly, giving less time for large crystals to form.

3. A granite with well-developed phenocrysts in a finer groundmass (a porphyritic texture) implies a two-stage cooling process:

   • Slow cooling at depth allowed phenocrysts to grow.
   • Then the magma moved closer to the surface, where it cooled more rapidly, forming the finer matrix.

In order to log a find against this EarthCache, you will need to visit the memorial and answer some questions and then send your answers to me via my Geocaching profile or through the Messenger Facility

1 Examine the memorial and let me know what colour Granite this is.

2 Please let me know which minerals are present in the memorial.

3 In relation to the size of the Phenocrysts did this cool quickly or slowly?

4 Post a photo of yourself, your mascot or your pet in the memorial garden.