Mindat Logo
bannerbannerbannerbanner
Welcome!

Beach Rocks (Plutonic?)

Posted by P. Michael Hutchins  
Beach Rocks (Plutonic?)
February 26, 2012 08:40PM
(I couldn't figure out what forum to post this in.)

I collect mineralogically interesting beach rocks from a geologically-complex area around Boston (Marblehead). Some look to me like they're displaying flow banding; some, magmatic immiscibility. Some have ~micro-graphic granite~.
(the graphic texture is (almost) too small to see w/ the naked eye)

Some have almost agate-like bands w/ xls on one side, all swirling around (folded?).

And so on.

I haven't figured out even where to look for information about these / this kind of rocks.

My first question was:

What minerals would this ~magma~ have turned into if it had cooled slowly enough?

Now I just want to learn enough to be able to look at one of these rocks and read its story, tell how it formed.

(I'm not a geologist; just love geology, mineralogy, etc.)
(MIT: Pure Math, Computer Science)

I'd treasure advice on where all to look, what discipline(s) this might fit into, technical terms that would help in searches, etc.
avatar Re: Beach Rocks (Plutonic?)
February 26, 2012 10:23PM
Some photos would help. What you have might not even be igneous which is why photos of the specimens are needed. As far as information, just type in igneous rocks or something to that effect into Google, Yahoo, etc... Better yet, find a recent copy of a college petrology textbook and it will give you more information than you ever wanted to know.



Edited 1 time(s). Last edit at 02/26/2012 11:11PM by Paul Brandes.
avatar Re: Beach Rocks (Plutonic?)
February 28, 2012 12:02AM
    
I don't know if this can be of help in any way, but it looks interesting:

[www.bostongeology.com]

Vik
Re: Beach Rocks (Plutonic?)
February 28, 2012 08:58PM
Thanks, guys!

I was definitely remiss in not including any photos!

Here's one of each rock that I have out for this purpose. I can certainly make zooms if they'd help.
Attachments:
open | download - P2280015.JPG (294 KB)
open | download - P2280016.JPG (193.4 KB)
open | download - P2280017.JPG (99.7 KB)
avatar Re: Beach Rocks (Plutonic?)
February 28, 2012 11:47PM
Hi,

The first one looks like almandines in some kind of shist,
Third one is some variety of chalcedony, probably flint
Second... I am not quite sure. For sure it is sedimentary rock, I see a lot of calcite, I think it has grains, so maybe it is sandstone, or even limestone with grains.
Author:

Your Email:


Subject:


Attachments:
  • Valid attachments: jpg, gif, png, pdf
  • No file can be larger than 1000 KB
  • 3 more file(s) can be attached to this message

Spam prevention:
Please, enter the code that you see below in the input field. This is for blocking bots that try to post this form automatically. If the code is hard to read, then just try to guess it right. If you enter the wrong code, a new image is created and you get another chance to enter it right.
CAPTCHA
Message:
Mineral and/or Locality  
Search Google  
Copyright © Jolyon Ralph and Ida Chau 1993-2014. Site Map. Locality, mineral & photograph data are the copyright of the individuals who submitted them. Site hosted & developed by Jolyon Ralph. Mindat.org is an online information resource dedicated to providing free mineralogical information to all. Mindat relies on the contributions of thousands of members and supporters. Mindat does not offer minerals for sale. If you would like to add information to improve the quality of our database, then click here to register.
Current server date and time: September 2, 2014 11:46:49
Mineral and Locality Search
Mineral:
and/or Locality:
Options
Fade toolbar when not in focusFix toolbar to bottom of page
Hide Social Media Links
Slideshow frame delay seconds