August 24:—SAN ANTONIO, TEXAS: Retail show; Southwest Gem and Mineral Society of San Antonio; Sat. 10-5
Welcome to the GemologyOnline.com Forum
A non-profit Forum for the exchange of gemological ideas
It is currently Mon Sep 23, 2019 5:06 am

All times are UTC - 4 hours




Post new topic Reply to topic  [ 8 posts ] 
Author Message
 Post subject: Marco Campos-Venuti: Course on Microcrystalline Silica
PostPosted: Mon Jan 04, 2016 7:02 pm 
Offline
Site Admin
User avatar

Joined: Sun Oct 16, 2005 12:22 pm
Posts: 19837
Location: San Francisco
I just stumbled on a YouTube series by one of my most respected industry professionals:
Marco Campos-Venuti

Marcos Campos-Venuti wrote:
COURSE ON: MICROCRYSTALLINE SILICA
held in microvideos by Marco Campos-Venuti (in ENGLISH)

I present here an innovative educational project on the Genesis of Microcrystalline Silica phases consisting of micro lectures of about 20-60 minutes each (in english or italian). You can see and download from youtube just by clicking on the corresponding icon. It is a walkthrought, intended for each audience, through photos and explanatory diagrams, with a geological approach and strongly multidisciplinary. With this project I want to make available to everyone a collection of ideas and interpretations on the genesis of microcrystalline silica phases that have been developed by the author in recent years. Hoping that these ideas can serve as inspiration for other scholars to further development in the same direction, perhaps with different methodologies to facilitate interdisciplinary character that is so important for the advance of science.

First in the series:
Origin of Oceanic Jaspers


MICROCRYSTALLINE SILICA

(click on the links to watch the videos)

GENESIS OF JASPERS

1- Origin of Oceanic Jaspers
2- Origin of BIF (Banded Iron Formation)
3- Origin of Volcanic Stratiform Jaspers
4- Origin of Volcanic Massive Jaspers
5- Origin of Volcanic Rhyolitic Jaspers
6- Origin of Thundereggs
7- Origin of Jaspers on Fossils
8- Origin of Laminated Chemical Jaspers
9- Origin of Orbed Chemical Jaspers
10- Origin of Brecciated Chemical Jaspers
11- Origin of Jasp-Agates
12- Classification of Jasper


Top
 Profile  
Reply with quote  
 Post subject: Re: Marco Campos-Venuti: Course on Microcrystalline Silica
PostPosted: Sun Dec 04, 2016 6:25 am 
Offline
Gold Member

Joined: Wed Sep 02, 2015 10:52 pm
Posts: 1131
Location: Central Queensland, Australia
It's very interesting but between my somewhat dodgy speakers and his thick accent I can't understand half of what is being said :(


Top
 Profile  
Reply with quote  
 Post subject: Re: Marco Campos-Venuti: Course on Microcrystalline Silica
PostPosted: Sun Dec 04, 2016 7:15 am 
Offline
Gold Member

Joined: Wed Sep 02, 2015 10:52 pm
Posts: 1131
Location: Central Queensland, Australia
Ok, listened hard - thanks to Marco I now think I know what this piece of material I found the other week is. Picked it up in an area marked on the map as a rhyolite flow. I sawed open the piece and was confronted with what looked like some sort of strange fungal growth....

Image

A rhyolitic orbicular jasper? But then again, it does appear to have been a nodule rather than part of a flow. Thundereggs and orbicular jasper are abundant nearby, maybe it's some sort of thunderegg precursor, weathered out of tuff?


Top
 Profile  
Reply with quote  
 Post subject: Re: Marco Campos-Venuti: Course on Microcrystalline Silica
PostPosted: Sun Dec 04, 2016 4:04 pm 
Offline
Platinum Member
User avatar

Joined: Fri Feb 24, 2006 1:20 am
Posts: 2742
Location: Southern California, U.S.A.
Do you have any images of the orbicular jasper from that area Lefty? It sounds interesting.

_________________
Rick Martin

www.artcutgems.com


Top
 Profile  
Reply with quote  
 Post subject: Re: Marco Campos-Venuti: Course on Microcrystalline Silica
PostPosted: Sun Dec 04, 2016 4:16 pm 
Offline
Moderator
User avatar

Joined: Mon Apr 02, 2012 9:31 pm
Posts: 3375
Location: North Carolina
You should pick up a copy of his book if you can get your hands on it. When it comes to things that have directly to do with volcanology and associated volcanic and volcaniclastic rocks and their typical features I think the work is very strong. It seems to connect very well with what I've learned on the subjects (extremely limited vs what Marco knows of course) and plays directly into his specialty's strengths. I am not as sold on what he says about polymerization, but the book is absolutely worth getting even with that in mind.

_________________
https://www.etsy.com/shop/angryturtle


Top
 Profile  
Reply with quote  
 Post subject: Re: Marco Campos-Venuti: Course on Microcrystalline Silica
PostPosted: Sun Dec 04, 2016 10:31 pm 
Offline
Gold Member

Joined: Wed Sep 02, 2015 10:52 pm
Posts: 1131
Location: Central Queensland, Australia
ROM wrote:
Do you have any images of the orbicular jasper from that area Lefty? It sounds interesting.


Hi Rick.

This is the orbicular jasper from Mount Hay, near where I found the photographed piece above, as well as chalcedony, petrified wood et. It's referred to as "rainforest jasper", it a green rhyolite with numerous little swirls of agate embedded in it. Mount Hay used to produce a lot of thundereggs though the spot is pretty heavily dug over now. I think the little agates in the rainforest jasper were trying to become thundereggs but couldn't keep growing when the rhyolite solidified.

Image

Image

Image

I saw a coffee table made from the stuff which was quite interesting.

My bet is that this stuff will have other occurrences somewhere else in the close vicinity - though that might just be prospectors optimism :) Hoping for some cooler days over the next month or so when I can get up into this area for a look.


Top
 Profile  
Reply with quote  
 Post subject: Re: Marco Campos-Venuti: Course on Microcrystalline Silica
PostPosted: Sun Dec 04, 2016 10:39 pm 
Offline
Gold Member

Joined: Wed Sep 02, 2015 10:52 pm
Posts: 1131
Location: Central Queensland, Australia
Stephen Challener wrote:
You should pick up a copy of his book if you can get your hands on it. When it comes to things that have directly to do with volcanology and associated volcanic and volcaniclastic rocks and their typical features I think the work is very strong. It seems to connect very well with what I've learned on the subjects (extremely limited vs what Marco knows of course) and plays directly into his specialty's strengths. I am not as sold on what he says about polymerization, but the book is absolutely worth getting even with that in mind.


I'll definitely do that if I can find it - be easier to read than to listen.

Books aimed at fossickers tend to merely tell you where known, established fossicking areas for different minerals and gemstones are - they seldom delve far into the how and why things formed and why they are found where they are and what kind of geology might hold potential.


Top
 Profile  
Reply with quote  
 Post subject: Re: Marco Campos-Venuti: Course on Microcrystalline Silica
PostPosted: Mon Dec 05, 2016 6:51 am 
Offline
Gold Member

Joined: Wed Sep 02, 2015 10:52 pm
Posts: 1131
Location: Central Queensland, Australia
Had a quick dig through the couple of hundred or so pounds of material from the site, nearly all of which is some form of microcrystalline silica (I guess petrified wood is both a fossil and a microcrystalline silica?).

I had always thought it was at least 90% petrified wood with a smattering of other things. But after watching Marco's videos I think a lot of it is other stuff. The wood probably still makes up over half but I think there are a lot of jaspers, jasp-agates, moss agates and maybe even some obsidian that hasn't yet de-vitrified. My main problem is that I don't yet have a slabbing saw and I'm not a member of the club anymore so I've got mountains of material that has never been sawn up.

Do these look like a variety of snowflake obsidian? The surface is naturally very glossy and vitreous-looking, quite a bit more than the photo shows.

Image

Image

The back of the second piece has some orange and red chalcedony growing over it.

Image

All manner of things - including a bunch not photographed - a few of which may have some lapidary appeal. The majority probably don't but they definitely hold some geological interest and when I get the bigger saw I should slice a heap up and polish a face on them and put them in a mineral display for interest's sake.

Image

Image

Image

Image

Image


Top
 Profile  
Reply with quote  
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 8 posts ] 

All times are UTC - 4 hours


Who is online

Users browsing this forum: No registered users and 0 guests


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Search for:
Jump to:  
Powered by phpBB © 2000, 2002, 2005, 2007 phpBB Group
Gemology Style ported to phpBB3 by Christian Bullock