Zeolites of Lomba dos Pianos, PortugalLast Updated: 14th Jan 2015
By Rui Nunes
Zeolites of Lomba dos Pianos, Portugal
It's a beautiful and amazing place!
The name of Lomba dos Pianos disjunction is due to the prismatic basalt formation that is particularly evident here, reminiscent of organ pipes of some churches. The columns are arranged perpendicular to the cooling surface, which in this case correspond to the sill limits.
Lomba dos Pianos is a sill of basaltic composition, with small crystals barely visible to the naked eye. However, in the black matrix, stand out a few larger amphibole and pyroxene crystals. In the rock fractures can be observed white to pink zeolites with a radial fibrous aspect. Globular structures can be identified with natrolite and thomsonite. It’s even harder to find cavities where capillary globules arise on analcime and calcite. There are also references to specimens with stilbite, heulandite and stellerite.
In addition to the prismatic disjunction clearly perpendicular to the cooling surface (the sill limits), there is also spheroidal disjunction that causes scaling of the dolerite - the origin of this erosive phenomenon is in the presence of nearly perpendicular fractures that are preferred sites for water movement with the consequent rock alteration. It is determined as well as portions of rock roughly spherical in the outer core and an altered and relatively more "healthy".
Whenever I visit the Lomba of Pianos it’s like the first time... My first zeolites are from Lomba dos Pianos; I even think that my the best Portuguese zeolites were collected here.
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