Geologic sample photo 2

Here again we are drilling in Al-Namas, Saudi Arabia for geotechnical purpose and I am musing on samples for geologic purpose. Namas is a small town on the Arabian Shield. I still do not figure out the best catchy title for this blog series,
but I think the current name give me a wide range to blog about any geologic sample I could photograph, not only the core samples. From the first look I identify this rock as Granodiorite. Untill I notes that rectangle black phenocryst surrounded by fine crystals, a question pop a in my mind! could that be Andesite. The first look identification for rocks and minerals is an experience we need to gather it as a field geologists. 

1

2

3

4

5

Photo @GeoSelim

Tell me about your experience in identification rocks and minerals, and How did you gathered it?. All photos taken during diamond drilling on one site in Al-Namas, Saudi Arabia.