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Molten rock was here!

A cache by G&Jcaching Send Message to Owner Message this owner
Hidden : 04/17/2011
1.5 out of 5
1 out of 5

Size: Size:   not chosen (not chosen)

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Geocache Description:

This EarthCache is on a busy road, but there is a wide verge to pull off the road. Please take care if you have to cross the road.

Millions of years ago, deep within the Earth’s crust, rock melted and was squeezed into the existing rock mass. This molten rock material cooled slowly, forming veins of large crystals of the minerals quartz, pink feldspar, mica and other minerals. Many millions of years later, when these rocks were uplifted and exposed at the surface, geologists discovered them and named them pegmatites.

In some places these can still be seen as fresh (unweathered) rock. In other places, the elements of weather and water, have reduces these just to crumbling mineral piles.In some places, these pegmatites have been mined to obtain some of their minerals.

At this location you can see quite a fresh exposure of pegmatite. It contains a number of minerals, the most obvious being the silvery mica (Muscovite). Mica is a mineral that forms in sheets, and these sheets make up a “book” of the mineral. The sheets can be easily peeled off the book and these sheets are transparent. Another mineral here is the black mineral tourmaline - which is the state mineral of Maine.

Just a short walk away (N 44 00.252, W 070 40.126) is something very different. It is the remains of yet another time when molten rock was squeezed into the surrounding rocks - but this time is was cooled very quickly and formed the hard dark rock geologists call basalt. This has very different minerals than the pegmatite - and because it cooled quickly the minerals are so small it's almost impossible to see them without a strong magnifying glass.

To log this EarthCache you need to answer the following questions in a email to us via our caching name above. We always enjoy seeing pictures of people visiting our EarthCaches - but the photo is optional!

1. What is the width of the basalt?
2. What is the width of the pegmatite vein?
3. Do you think the width of these bodies might have influenced the size of the crystals in the rock?
4. What rock type do you think makes up the original bedrock that these two veins intrude?

Additional Hints (Decrypt)

Gur onfnyg irva vf guva!

Decryption Key


(letter above equals below, and vice versa)

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