Rocks

Rockhunter Northwest 

Felsic - "light" rocks, contain light colored minerals (Also low temp minerals See Bowen's Reaction Series above) (quartz, Potassium feldspar, micas) 

Mafic - "dark" rocks, contain dark colored minerals (Also high temp minerals See Bowen's Reaction Series above) 

(Pyroxene, Amphibole, Calcium Plagioclase) 

Mahogany Obsidia

 

Rock hunting 101 ... collecting Oregon Coast agate and 15 million year old fossil mollusks

Granite breakdown, How granite is formed

25 Most Common Rocks on the Beach: How & Where to Find Them?  

PNW beachcombing 

Picture Identification Guide for Polished Stones and Tumbled Rocks  

Dunite