This cache is in Mahon Park at one of the Jones Ave. entrances. It is the large boulder with the plaque. This cache is to illustrate the mineral hornblende, a very common rock forming mineral which you have probably seen many times while looking at granitic rock. There are about 5 common minerals which make up granite and this is one of them. (mica, quartz, feldspar, augite, hornblende)
All the small black specks on the face of this rock are hornblende. Hornblende is a field and classroom name used for dark-colored minerals found in many types of igneous and metamorphic rocks. Hornblende is the name of a group of minerals which all look the same and can only be seperated under a microscope. The specks look a bit like pepper on the light colored granite face.
This is what a common hornblende granite rock looks like. Black specks are hornblende.
Also on the rock face are about 12 dark angular brown xenoliths which are foreign rocks which broke into the rock soup when it was a liquid. These xenoliths are not the subect of this cache.
Your job to log this cache is to tell me either by email or messenger the following.
1 The number of black specks on the rock face you see, is it tens, hundreds, thousands or tens of thousands.
2 What do you think the most common shape of the black mineral is. You will have to look closely at several specks and decide. Like round, square, elongated or just random.
3. Estimate the size of the average speck in mm.
4. And just to make it more complicated, what is the last name of the lower right person on the plaque. His first name is Craig.