Tremolite and actinolite are almost always found together as they are a solid solution series.
It is more complicated than what follows but this is the general gist: They are products of both tectonic and intrusive igneous activity induced metamorphosis-- by hydration, of host rock which may have originated in mantle/deep crust)-- in the case of actinolite, serpentine and tremolite. Tremolite may also be derived from dolomitic and other carbonate rock which was down warped into a high temperature zone. All are typically brought back to the near surface by tectonic activity(uplift/thrust faulting)-- but at some pressure/temperature junction circulating high thermo water forces molecular change by adding the hydroxal.(^-OH)
Tremolite and actinolite are a mineralogical "solid solution" after amphobole and pyroxine which may be derived from either ultra-mafic granite OR "psudo-marblized" dolomite. Serpentine is hydrated olivine. Tremolite , actinolite and serpentine are the hydrated (^-OH) counterparts of Amphobole, Pyroxine and Olivine(Fayalite/ Forsterite) If recollection serves.
To further add complication, tremolite can proceed to dopsite under higher pressure and actinolite can spawn jadeite and nepherite. It all depends on when nature takes it out of the oven, so-to-speak. By studying the "mix", a general pressure/thermal history can be deduced. More complicating is retrograde metamorphism and formation of garnets etc. There are whole books just on tremolite/actinolite multiple "origins and destinations".
One more facet: tremolite and serpentine can form tremolite-asbestos and crysotile-asbestos, respectively.
Eman
From: "Kim Noyes kimnoyes@gmail.com [geology2]" <geology2@yahoogroups.com>
To: Geology2 <geology2@yahoogroups.com>
Sent: Friday, July 10, 2015 2:32 PM
Subject: Re: [Geology2] Volcanic rocks resembling Roman concrete explain record uplift in Italian caldera
Actinolite? I collected that as a child in the Cajon Pass of San Bernardino County where it washed to from a deposit up the mountain near Wrightwood, CA. I've also collected it from various locales in Mendocino County with my ex-girlfriend. There is also some to be found with the jade and serpentine of the Big Sur Coast. It seems to me that it would not geologically and chemically be something that could form in an active tectonic belt but rather in a more metamorphic regime..... I find this curious but fascinating. aly's dormant Campi Flegrei volcano are similar to a wonder-material used by the ancients to construct enduring structures such as the Pantheon, and may lead to improved construction materials.
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