|
Post by snowmom on Jan 8, 2015 6:42:01 GMT -5
maybe this question will need a geologist. I am interested in the similarities of certain rocks I have found in this area. They are all glacial erratics, all lake and weather worn, all very tough and dense. They seem to have a pattern of graining which goes in one direction, and then another pattern that is usually not quite 90 degrees, imposed or combined, going the other direction. I have associated this with serpentine in my mind, but read everywhere that serpentine is quite soft, and these all seem to be 5.5 mohs and some much harder. Most seem to have a high specific gravity for they are very heavy for their size compared to rocks I am sent from RTH members in other locations. I don't know if this is a product of serpentization, of perthitic interactions (yes, perthitic formations can be visible to the naked eye and are not only happen on a microscopic scale) Most of these rocks seem to have high epidote/olivine content along with orthoclase feldspars some seem to have a bit of quartz as well. High iron and silica content is common here due to the water being saturated with both elements. I am interested if this cross textured pattern is serpentization (alligatoring) or if it is some other process, and if so, what would that process be? Since these are all dense and hard, would they then be considered serpentinite?
Can you see by looking, the pattern I am referring to?
|
|
|
Post by snowmom on Jan 8, 2015 6:51:51 GMT -5
|
|
|
Post by broseph82 on Jan 8, 2015 9:58:11 GMT -5
I bet you have the most colorful yard (house) on the block.
|
|
|
Post by snowmom on Jan 8, 2015 15:09:34 GMT -5
jimi, they're all my pets, I keep them in the house. Good thing they never ask to go out and I don't have to feed them!
|
|
|
Post by 150FromFundy on Jan 8, 2015 16:52:57 GMT -5
Those rocks appear to be Epidosite which is a rock containing Epidote and Quartz. Epidote ranges in colour from pistachio green, green, blackish green, brown and light yellow. Epidote has a hardness of 6-7 and a specific gravity of 3.4 to 3.5 which is why they are heavier than quartz (2.7).
Epidote is associated with metamorphic rocks. Metamorphic rocks are typically foliated which would explain the patterns. Epidote and Epidosite are extremely common.
Serpentine is much softer (2 to 5) and much lighter (2.2 to 2.6) and should have a waxy or greasy feel. In order for serpentization to occur, you have to start with serpentine, which I don't believe you have.
I'm not a geologist and books can be dangerous, so I could be going down the wrong road on this one.
Darryl.
|
|
|
Post by snowmom on Jan 8, 2015 17:00:41 GMT -5
Thanks Darryl, Yes I do believe most of those rocks have epidote/olivine to a great degree, most of the glacial erratics I find here seem to be loaded with it. The S.G. of epidote would explain a whole lot and I would not have figured that one out if you hadn't pointed it out. (duh!) Thank you so much. It seems to be everywhere in great abundance, so that is another argument in favor of all those greens being olivines/epidotes. I don't get tired of all the greens though. Any idea what process would cause that texturing? Is it the massive form of crystal structure for olivines? gotta go do some digging, you started something here (thank you!)
|
|