At this spot in this historic Salem park you will find some great views, and some very interesting rock. The rock you are looking for has porphyritic syenite veins with mafic trap dykes. What’s that you say? Let’s break it down…
Porphyritic - Seen in igneous rock, this is where large crystal structures are embedded in a finer grained rock with smaller crystals.
Syenite - A coarse-grained intrusive igneous rock, similar to granite, but with less quartz
Vein - A sheet of crystallized minerals embedded in rock which forms when and existing crack in a rock is filled with a different mineral
Mafic - an adjective describing the amount and kinds of silicates in igneous rock. Mafic rocks contain higher amounts of the minerals rich in magnesium and ferric oxides which usually results in a darker grey color.
Dyke - A sheet of rock that formed in a pre existing crack in another rock. This sheet can be igneous rock or sedimentary and is usually found in a near vertical orientation, but it can be found in any orientation if the rock changed orientation after it was formed.
These words describes the darker rock you see here with the light colored lines. The Dyke in this case is the darker rock. Look over these rocks, there are a lot of interesting things happening here. In a few spots, you can see that some of the rocks are wearing away at slightly different speeds. Note: these formations lie near the high tide line in beverly harbor, and they may be difficult to access at high tide, or even impossible during unusually high tides. You may like to consult a tide chart.
To claim your find, send me the answers to the following questions:
1: Which came first, the dark colored dyke or the light colored veins?
2: What size are some of the larger crystals in the Porphyritic rock?
3: Which contain harder rock, the dyke or the veins?
4: How can you tell? (hint, the easiest way to answer this is observation at GZ)
5: Include a photo of you or your GPS at ground zero with your log. (optional)
Congratulations to Bumble! on the FTF!