Hi!! I believe its due to the different minerals and layers of sediment, though i'm no Geologist and google hasn't been too useful :/ I would highly recommend a visit - not only for the mountain but for the scenery all around :)
The App i use is OS locate - Its a great app designed to help obtain grid references for OS maps in the UK, however when you use it outside of the UK it gives you a GPS reading ;)
So cool. Thank you for the pics and the info abot the app. I now have a new destination for my travels (:o)