FMF - Friends of Minerals Forum, discussion and message board

[tsaintonge]

So we just remodeled our kitchen and picked up a really cool and unique granite slab(s). The slabs have some interesting and varied formations and we were hoping someone better equipped than us could take a look at these pictures and help us identify the makeup. My wife teaches elementary science and thought we could use this as a fun side lesson in her class as well.

This particular granite is called Sierra Nevada, and the country of origin is said to be India.

Please see the attached pictures, but as you'll see, there is an overall white color tone with accents that include...
- sections that look like quartz?
- sections that are gold and "glittery"
- splotches of something 'jet black'
- a couple small areas that almost look like charcoaled wood
- a few small splotches of Navy blue.
- etc, etc, etc

Thanks in advance!

[Matt_Zukowski]

The mottled grey mineral in 20211025_215604.jpg and 20211025_215836.jpg is quartz.

The golden platy mineral in 20211025_215743.jpg and 20211025_215815.jpg is muscovite.

The black platy-looking mineral in 20211025_215506.jpg is biotite if it is indeed platy.

The black mineral in 20211025_215527.jpg could be biotite or hornblend. One of black minerals in this picture looks like it could have a hexagonal shape, which would suggest tourmaline, but i doubt it - it is probably the same mineral as the black more tabular mineral next to it.

The white material is feldspar.

[Peter Lemkin]

While it is granite, it is a slice through a special type of granite called a pegmatite. I suggest you look that up on the internet. There are different types of pegmatites and different minerals in different pegmatites [or areas of one pegmatite], the basic feature is very large grain/crystal size and a concentration of some rare elements and compounds. I have a whole library on pegmatites. If you are really interested in knowing about your tabletop and have a scientific background, I can give you a few references that are fairly technical; but you will find a lot about pegmatites on the internet. They are one of the most fascinating mineralogical formations and where many [not all by far] nice and large mineral specimens/crystals come from. When I go out collecting minerals I often head to pegmatites. Your table may just start you in the direction of mineral collecting......

Technical, but about the best single book on the subject [IMHO], is Pegmatites by
David London Volume 10, 2008
ISBN: 978-0-921294-47-4
Pegmatites gives us an excellent and thorough review of the current state of the art in pegmatite studies.
In Part I, Geology, London provides a primer on the mineralogy, geology, and classification of pegmatites. But the center of gravity of this treatise is in Part II, Origins, which consolidates London’s petrological model of internal pegmatite evolution, and compares it with other concepts.
https://www.mineralogicalassociation.ca/publications/special-publications/sp10/
(link normalized by FMF)

But there are many books and articles for the lay reader on the subject and perhaps the best place to start. If and when you can read and understand London's book, you could write your own book just about your tabletop.

[James Catmur]

A nice slice of pegmatite within granite. The list of minerals provided above makes sense.

This forum tends to focus on crystals, so if you use FMF gallery search (at the top of this page) you may find examples of these minerals. For example (searching on Euclase, which was not listed above)

https://www.topminerals.info/index.php?searchterms=Euclase&searchauthor=-&level=search

You can also search a sister forum called Mindat for photos of examples of those minerals. So search on “Mindat Euclase” and you would find:

https://www.mindat.org/min-1418.html

For Biotite you would see

https://www.topminerals.info/index.php?searchterms=Biotite&searchauthor=-&level=search

And

https://www.mindat.org/min-677.html

[tsaintonge]

Thanks guys - some great info so far.

Matt - you pointed out that the Gold sections appear to be muscovite, and from looking at images, I agree!

Peter, I looked up some images and tried to find info pertaining to this slab ... based on what you said (and Matt pointed out) I believe it's 'possible' that this piece may have been sourced from/near Andhra Pradesh, India. Looks like there's a large quarry industry near there.

So my own kids, and my wife for her class, have some follow up questions. Based on the type of minerals found grouped together in this specific slab... and without carbon dating... is it possible to get obtain a more specific location of where the piece was sourced, and/or, a general age of the material? I'm sure that a chunk of muscovite compared to another, without specific testing, would be indistinguishable. However, when looking at this piece as a whole, and considering the materials contained together, are you able to make an educated guess?

And, is there a type of geological activity (specific) that would have been occurring at the time, to have created this specific group of minerals to combine and form this section?

--- I know that's a lot of questions, but this simple 'granite' slab has really sparked some interest!

[Peter Lemkin]

[tsaintonge]

[Peter Lemkin]

Sorry, you think your questions have simple or short answers. Most do not. I am not going to try to explain 'intrusives' or pegmatitic intrusives. There are papers, books and I'm sure websites on that. Maybe someone else here has the energy for that question. I do not.

My final response to you would be to go to a very important website and start on this page: https://www.mindat.org/loc-24472.html
It shows 75 important mineral locations in that state of India...I'm sure not all pegmatites, but look through them and find those that are and see what you can find out using the internet. Lovely photos and other information is available on that website [and others].
You might try putting 'pegmatites of Andreh Predesh' and see what you find.

Good luck. Rome was not built in a day, and by the end of this day you will not know all there is to know about pegmatites I'm afraid. They have been my interest for 65 years.

[James Catmur]

See if you can find a second-hand copy of 'Minerals: An Illustrated Exploration of the Dynamic World of Minerals and Their Properties', as I recall that it has a fairly good, but simple,explanation