Starting to think about types of granite

 

This diagram is from Wikipedia - see here for full attribution. I've got my head round the top triangle which deals with the minerals in granite. The Q at the top is Quartz. The A on the left stands for Alkaline feldspar minerals. Feldspars seem to be based on aluminium silicates but can have sodium or potassium in making them Alkaline feldspars. But some have calcium in, which is the Plagioclase feldspar P on the right. As you can see in the diagram, granites contain more alkaline that plagioclase in general and are 2/5 quartz. Potassium feldspar is pink. Looking at the picture in my last post, the pebble on the extreme right is very pink. The looks like it might be alkaline feldspar granite. If I can get my head round the types of granite, I am hoping to work out the original source of the pebbles.