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Orange & grey crustose lichens, aqua-green foliose lichens, moss and a few grasses and ferns colonizing 1.2 billion-year old columnar basalt serving as a natural breakwater at Grand Marais, Minnesota.
Many of these species are Arctic disjuncts, but can eke out a living among Lake Superior's cool climate where protected from wave action and trampling by people.
This porphyritic basalt comes from the Isle Of Mull, where volcanic activity took place in the Tertiary era, around 60 million years ago. If a magma cools slowly underground large crystals will form in it, the highest melting point species being the first to solidify. If this magma is then moved to the surface, as a lava, or even near the surface, as a minor intrusion, the remaining met solidifies quickly resulting in a groundmass of fine crystalline material. Thus one ends up with a fine grained rock studded with larger crystals, called phenocrysts. The term for this lumpy texture is porphyritic. The large crystals, called phenocrysts in this context, consist of larger grey feldspars and smaller black pyroxenes.
diff version
my lichen photos by genus - www.flickr.com/photos/29750062@N06/collections/7215762439...
my photos arranged by subject, e.g. mountains - www.flickr.com/photos/29750062@N06/collections
The discovery makes Nan Madol a key locale for studying how ancient human societies evolved from simple societies to more complex societies, said SMU archaeologist Mark D. McCoy, who led the discovery team. (Credit Helen Alderson)
Project 7x52 - Week 6 - Objets d'Art.
#5 – Basalt II: This detail shot of Brad Hall’s Basalt II shows the rusty patina developing.
Overview: There are many aspects to the Historic Gardens that are of interest each and every season. Many of them are made of metal, and these are the ones I have chosen to feature in Week 6 of Project 7x52.