A Pittsburgh Area Mineral, Fossil, & Lapidary Club
The Monongahela Rockhound News is a Monthly Publication of the
Volume 53, Issue 2,
Visit us on the Web at: www.monongahelarockhounds.org
Our next meeting will be held this coming Saturday, February 1, 2020 at 7:30 pm, in the Munhall Borough Building.
Johanna Burnett will do a presentation.
Hosts for February will be: June/Bret & Carol/Frank.
February minerals: Agate & Jasper
Dues are Due!
The new year is here, and that means that memberships need to be renewed. Dues are $10 for an individual, and $20 for families plus an additional $10.00 if you want your newsletter mailed (instead of e-mailed). Please bring your check to the next regular meeting. We also need a signed membership form with present e-mail address and contact numbers to keep our records current, plus for insurance coverage.
If you joined after September 1, 2019, your membership is valid through December 2020.
• Presentation by Johanna Burnett
• "Rock of the Month" will be Agate & Jasper
• Hosts will be June/Bret & Carol/Frank
Feb 01, 2020, 7:30 PM – 9:30 PM EST
Munhall Borough Building, 1900 West St, Munhall, PA 15120, USA
4 January 2020
By Frank DeWinter
Instead of a presentation, Gerry Gagorik organized a “White Elephant Gift Exchange”. Fun was had by all.
June Epp conducted the business meeting on behalf of Johanna Burnett.
Attendance was 32 adults and 3 junior members.
Show-and-Tell was tourmaline:
Gerry G showed cut & polished petrified wood & opalized wood.
Gwen F showed Petrified wood & Ammonite Jewelry.
Don L showed a petrified palm wood bowl he had carved and a red cylinder he had made from red jasper.
June E showed Goethite cubes she & Bret had found in a Carrol Co rock cut in Maryland.
Bret showed a large piece of petrified Palm Wood form Louisiana and an opalized tree limb.
It was identified that during our November election we had forgotten to elect the new board of directors. Don Laufer and Frank DeWinter were elected to the board.
Tony presented the treasurer’s report.
Bret gave a report on our upcoming show to be April 18 & 19. Everything is basically organized, with dealers and contracts in place.
A motion was made by Frank DeWinter, as the editor, “to keep the present membership dues at $10.00 for individual and $20.00 for families for membership where the newsletter is e-mailed only, but to add an additional $10.00 for either individual or family membership if the newsletter is to be mailed out to cover a portion of the printing and postage costs.” Tony Orzano seconded the motion. After discussion, the motion was voted on and carried with 20 for and 1 against.
A suggestion was made to have everyone wear name-tags next meeting because of the high number of new members.
We had 9 new members at the meeting, including Denise, Bonnie, Imogen, Keri, Robin, Judi, Dave Kari, David & Seth.
Thank you to both Gerry G & Gwen F for hosting refreshments in January.
Next month's presentation will be by Johanna Burnett.
No one initially volunteered to do a newsletter article.
Rock of the Month for February will be Agate & Jasper.
Hosts for February will be June/Bret & Carol/Frank.
Monongahela Rockhounds PO Box 18063 Pittsburgh, PA 15236 www.monongahelarockhounds.org Mission Statement
To promote, among its members and the general public, an interest in collection of minerals, fossils, and associated items.
To promote their use in lapidary work.
To promote the study and classification of minerals, gem stones and other items of such nature.
Member: Eastern Federation of Mineralogical and Lapidary Societies, Inc.
Member: American Federation of Mineralogical Societies, Inc.
Meeting Location Munhall Borough Building 20th Ave. & West Street Munhall, PA 15120
President Johanna Burnett 1st Vice-President Bret Howard 2nd Vice-President Debbie Braddock Treasurer Tony Orzano Record Secretary Debbie Thompson Silent Auction Debbie Braddock Board of Directors June Epp Donald Laufer Frank DeWinter Webmaster Emmalyn Ilagan email@example.com Newsletter Editor Frank DeWinter firstname.lastname@example.org
We normally meet the first Saturday of every month from September through June at 7:30 pm, in the Munhall Borough Building for a presentation, business meeting and a chance to socialize. There is a major focus on the younger members of our club with portions of the meeting specifically for school aged children. Our next meeting will be on Saturday, February 1, 2020. The March meeting will be on the 7th.
Monongahela Rockhound News is the official newsletter of the Monongahela Rockhounds.
Disclaimer & Release: To the best of our knowledge, all articles and information presented in this newsletter are true, accurate and free of copyright infringement. The Monongahela Rockhounds is not responsible for the usage of the information contained in the newsletter. The Monongahela Rockhounds hereby grants other non-profit organizations the right to republish articles in this newsletter for non-commercial usage as long as complete source credit is given, unless noted otherwise.
Deadline: The editor welcomes any and all contributions to the newsletter. Please provide articles and any other submissions for publication at least 2 weeks prior to the upcoming meeting to be considered for inclusion in that month’s issue.
Please e-mail any newsletter articles to the editor's e-mail: email@example.com
By Bret Howard
A Very Brief Overview of Agate
So what is an agate exactly? For most rock collectors, the word agate brings to mind an oval rock with concentric bands of different colors. This is, in general, correct but “agates” are a much larger and very interesting group which is actually somewhat difficult to define exactly. What an agate is depends a lot on who you ask or what reference you refer to. In general, agate is cryptocrystalline quartz (more information on this below) that shows some type of banding. It can be found in many shapes such as hollow geodes, solid agate nodules, crack or crevasse-filling veins, and filling many other types of voids in rocks. Sizes can range from below a centimeter to well over a meter. It is also very common and can be found in almost any country. However, there are some varieties and locations that are especially noteworthy and will be mentioned below. Under the heading “agate” on Mindat.org, there are currently 3048 agate photos. This is a good online source to get an idea of the varieties of agate found worldwide. Agate is also very common in the United States and some type can be found in almost every state, even Florida. Some confusion is introduced as to what an agate is by the use of the term for rocks that don’t meet the banding criterion such as moss agate and fire agate. Moss agate typically does not show banding. The patterns seen are caused by dendrites of other minerals in the chalcedony matrix, usually manganese oxides. Fire agate is another variety of chalcedony that shows an iridescent “fire effect” due to inclusions of various iron oxides.
Uses and history
Agate has been recognized and used for thousands of years. The Egyptians and Romans used it to make decorative items and in jewelry because of its hardness and attractive colors. It was often used to make stamps for embossing wax seals. As we have heard in previous club presentations, Idar-Oberstein, Germany, was and is famous for its artistic agate works which originally utilized locally mined rough agate. Agate has also been used to make marbles, known as “aggies”, which are popular with marble collectors. Because agate has a very slightly porous structure, it can be dyed to introduce much brighter colors – the bright greens, blues, pinks, etc. often seen for sale at mineral shows. This is often done to make lower quality agate more marketable. Also, its hardness and toughness makes it attractive for some industrial uses. It is often used in laboratories in sample grinding instrumentation such as mills and mortar and pestle sets.
Composition and structure
Agate is a variety of chalcedony as are jasper, flint, carnelian, chert, chrysoprase, flint and others. All of these varieties are primarily composed of cryptocrystalline quartz which means that the quartz crystals that make up the rock are so small that the individual crystals can’t be seen without the aid of a microscope or other technique. Agate is primarily composed of quartz but almost always contains other mineral components. It often contains several percent moganite which is a silica polymorph – SiO2 with a different crystal structure. The colors observed in agates can be caused by several different mechanisms; light scattering through the structure, atomic substitutions in the quartz structure (amethyst, for example) and the inclusion of other minerals between the microscopic quartz crystals (iron oxides, for example). The third mechanism gives many agates their bright colors. As mentioned above, the primary characteristic that sets agate apart from other cryptocrystalline quartz varieties is its banding. However, a second structural characteristic is present in agates that is not always found in the other group members – the structure contains “fibers”. The fibers consist of aligned microscopic quartz crystals. These fibers tend to be oriented parallel to each other and radiate from the wall towards the center of the cavity that the agate formed in. The fibers are not normally easily observed. However, in thinly sliced, somewhat transparent agate slices, the oriented regions can be visible when back-lit. This can make an interesting optical effect! This description of the composition and structure of agates barely touches the subject which has been and continues to be studied. (And the subject of the growth of agates hasn’t even been mentioned here!)
Noteworthy agate varieties
Agates are found virtually everywhere but some “varieties” and locations are better known. These better known types are usually due to some desirable characteristic such as attractive coloration or interesting banding patterns. United States agates include Lake Superior agates, Tampa Bay agatized coral (sometimes exhibits banding), Utah and Oregon Thunder Eggs. One exceptionally interesting variety comes from the copper mining region in the Upper Peninsula of Michigan. These agates often contain copper and copper oxides in the banding giving them a unique appearance. Mexico is known for a number of agate locations such as the famous, brightly colored Laguna agates, Moctezuma agates, and, of course the Chihuahua geode bed agates. Other well known worldwide locations include Botswana (Botswana agate with fine pink banding), Rio Grande do Sul, Brazil produces literally tons of fine agate, Paraíba, Brazil (the source of the unusual Polyhedral agates found in the 1970’s), Agate Creek, Queensland Australia (brightly banded agates often with yellow and greenish coloration), and Morocco (currently producing a lot of agate which often has nice red banding). This list doesn’t begin to cover the agate producing countries around the world. The large number of locations and varieties to be found is what leads some collectors to concentrate on agates for their collections.
Online sources: Mindat.org, “The Quartz Page” (http://www.quartzpage.de/intro.html) There are many books written on agate. Some cover the varieties of collectable types and some the science.