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Santa Rosa Mineral and Gem Society
SRGMS Newsletter Nov & Dec 2010

Twinning in Crystals

by Bob Carnein, Lake George Gem & Mineral Club
From: Lake George Gem & Mineral Club News, 8/09
(4th Place - AFMS Adult Articles Advanced)

Anyone who is interested in minerals and crystallography will eventually encounter twinned crystals. My introduction to twinning occurred when, as a 12-year-old, I collected staurolite crystals from the classic garnet/staurolite locality at Roxbury Falls, Connecticut. Younger readers may have seen the beautiful staurolite crosses from New Mexico, for sale at the Contin-Tail Show in August, or the Russian staurolites sold at most shows and on the internet.

Closer to home, many Colorado localities, including the Crystal Peak area, produce spectacular feldspar twins. Cripple Creek is noted for twinned crystals of the cold-silver telluride, sylvanite, and Mt. Antero has rare twins of the beryllium mineral phenakite. All of these sell at a premium when available.

New collectors often are unaware of pitfalls they need to avoid when they are offered a twinned crystal. Search eBay and other sources, and you are likely to find dozens of "twins" that are, at best, products of an over-active imagination, or, at worst, attempts to deceive. Minerals commonly sold as twins include the feldspars, staurolite, and phenakite, as well as aragonite, beryl, chrysoberyl, calcite, cinnabar, garnet, pyrite, quartz, rutile, tourmaline, and others. Although some of these form twins, others do not. So, how does one distinguish a true twin from a fake?

First, let's consider a definition. According to Klein (2002), twinning is "a symmetrical intergrowth of two (or more) crystals of the same substance." Notice that if three or four crystals are intergrown, we don't call them "triplets" or "quadruplets." They are still twinned crystals. Note also that twinning is a special kind of intergrowth, and this is where problems commonly arise. Those who attribute magical properties to crystals often seem to think that any two intergrown crystals are twins and so have special "powers." Although I can't comment about crystal magic, I can assure you that for every kind of twin there is a twin law that governs such things as the angular relations of the individual crystals and how their symmetries relate. Twins most definitely are not random intergrowths. Ultimately, all of this relates deeply and precisely to the arrangements of atoms and ions in the crystal structure.

Two broad categories of twins are contact and penetration twins. Contact twins consist of two or more crystals joined along a plane or planes of contact (called composition surfaces). Examples are Manebach and Baveno twins in microcline, Japan twins in quartz and spinel twins in spinel, copper, and galena. You can clearly distinguish the composition surfaces in each of these. Interpenetrating crystals characterize penetration twins.

Twins also can be described as simple, where only two crystals are involved, or multiple, if three or more crystals are intergrown according to the same law. If all of the composition surfaces are parallel, multiple twins are said to be polysynthetic. Examples include plagioclase feldspar, in which polysynthetic twinning causes the striations that provide a near-certain clue to the mineral's identity, and in some calcite that has been subjected to pressure during or after crystal growth . Multiple twinning along non-parallel composition surfaces is called cyclic twinning.

Sometimes twinning is obvious even to the beginner, and, at other times, it is subtle and unlikely to be noticed. Japan-law twins in quartz, the cross-shaped twins in staurolite, and Carlsbad twins in microcline fit into the former category. These are all simple twins, and the two crystals involved are clearly visible. However, most quartz exhibits Dauphine twinning, in which the only obvious clue may be offset striations on the prism faces (the flat surfaces parallel to the crystal's long axis). Only rarely is Dauphine twinning obvious. Many aragonite crystals have a roughly hexagonal outline because they are cyclic twins made up of three crystals that are intergrown. Many beginners think aragonite is hexagonal, but, in reality, it belongs to the orthorhombic crystal system.

Twinned crystals constitute a rare, fascinating category for the mineral collector. Keep your eyes open, and you might find a beautiful twin hidden in a dealer's stock at a show or in one of the gem "pockets" at Crystal Peak. They're well worth the search.


Membership Fees:

Individual $40
Family of 2 $60
Additional $20
Jr. no Parent $20

Membership is good for one year from day you joined. For more information call (707) 528-7610 Leave a Message.


Welcome New Members:
Angelina Artemoff & Win Myerson
Rowan Artemoff-Myerson
Alexis Biasotti
Gianna Lovell
Richard & Sharon Sibbet
Greg and Justin Small
Richard & Catherine Williams
Caitlin Williams
Lori and Rich Anderson
Taiven Fosnight
Elijah Kinses
Bill Miller
Suzie Lennon
Marcia Sandler
Ashley & Matthew Simmons
Tami Ward
Peter Zimmerman

SRMGS Meetings:

We love to have more active members. Attend one or more of the SRMGS Meetings to get the most out of your membership! Meetings are held at the SRMGS Workshop.

General Educational & Potluck Meeting

Wednesday Dec 1, 2010
6:30pm
Holiday Pot Luck & White Elephant Exchange

SRMGS Board Meeting:
Thursday Dec 9, 2010
7:30


Announcements:
Gearing up for Quartzsite Rock Show come January.. you going?


SRMGS Websites
SRMGS has two websites www.SRMGS.org for resources & group information, as well as www.Gem-N-i.org for an archieve of our monthly newsletters.

Make submissions to the site by emailing news (AT) gem-n-i(dot)org by the 16th of the month or catch me at the next meeting at the shop.


Tips & Tricks:
Tumbling Tips - In my quest to achieve a perfect tumble on obsidian - Steve suggested using broken auto glass (you can get from auto body shops) to mix with your grit. Since I was having trouble locating that, I opted for clean "white sand" purchased at hobby shop. Final polish was done using crushed walnut shells and soap.
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.: The Gem-N-I Revisited :.

Canada Trip
by Jim Fitch 10/74

In late July we took off with our trailer for a six week trip to central British Columbia. It was primarily a fishing and outing trip in some of Canada's most beautiful country. However, we found that our rockhound interest played a major role in our activities and pleasures.

Our headquarters were established at Francois Lake, a lake some 90 miles long, located between Prince Rupert and Prince George. This is a fine fishing lake as well as an excellent area for collecting many fine types of agates and fossils.

We took time out during the trip to visit the many rock shops along the way. Here we could ask for information about local minerals as well as examine their local work and specimens. In fact, we were able to pick up some excellent jade from a shop in Prince George and traded with several of the rock shop owners at various places along the way.

We found some nice agates along the shores of Lake Francois. Some were clear as water and others were banded with various colors. We also found the prized carnelian agate.

An interesting mineral area is described in the B.C. Gem Trails book. This area is located a short distance from our camp, so we decided to investigate it. The area claims to be one of two locations where collinsite can be found. Our enthusiasm was somewhat cooled when we found the area had changed hands and the new owners could care less about collinsite. We did obtain permission to visit the site and do some digging. Our find were very meager and disappointing. The collinsite turned out to be something between plain coal and obsidian. The book was published in 1973, but the information was somewhat obsolete.

From the lake we took an intersting side trip to the fossil beds near Smithers, an intersting and busy lumbering center. We followed a stream bed to an enormous shale canyon where many types of fossils are found. The shale cliffs were pretty well worked over, but slabs of shale were easy to work from the cliff and were then split open for specimens. We were lucky to find many interesting leaf patterns from sequoia, willow and alder trees.

Our return trip took us through the Oregon country along highway 97. Here is indeed a land of many minerals, particularly agates of all types. Our stops salong this route proved interesting and fruitful as we were able to pick up many types of rocks.

Now we are busy with the slab saw, seeking out the good pieces and throwing out the "duds". In the near future I hope to have a fossil collection to show to our group.

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A lil Eye Candy

A Message From Kendra.
SRMGS Webgirl
DEAR GEM-N-I READERS:
The Holidays are officially here, I say that as pumpkin pecan pie is in the oven and I'm starting the prep for other goodies for the big feast. I've decided to combine the last newsletter as it took me several weeks to focus on stuff after the show. Speaking of which, THANK YOU to everyone who helped out! This year's show was amazing! We made some changes and everything seemed to be well recieved by the public and the vendors alike.

December is our Pot Luck Party, we will be annoucing our new board members, sharing food, and playing the silly rock /gift exchange that is a LOT of fun!! I plan on making butternut soup and lattes, if you want to try it, you have to be there! :D

On a final note, this will be my last newsletter. As mentioned before I really appreciate everyones support over the past 3 years, I have learned so much about rocks, minerals & local geology that I can fool people into thinking I know what I'm talking about. It's really been informative, interesting, and actually fun doing some of the "research". I can honestly say, a rock is no longer just a green pretty rock. Thank you!!
~Kendra

Thank you!!
Big thank you to:
Lynn - Flat Lap Kendra - Snacks Joel - Saw Cover Pattern
Shop News
Congrats & Thanks to Jim H. as our new shop foreman! His talents and enthusiasm are both welcomed and appreciated.

100 & 220 grit wheels have been ordered
Saw Oil has been ordered
Saw #1 - Jim is having parts machined for it
Saws #2-5 are desperate for cleaning, to prevent motor burn out. If you don't know how to clean a saw, ask the shop attendant.

Are you DUE?
Friendly reminder that the following annual SRMGS memberships will expires this month. Please fill out the renewal application and mail your payment. The following are due this month:

Wendy Dayton
Kathleen Sherman Mariana & Isabella Leal
Shirley Mattson
Ashley Remilliard
Erica Tanner
Ethan Williams
Virginia Young
Brenda, Reilly & Michael Holmes
Steve Kemmerle
Dan Nielsen
Cindy Baldwin
Reid Reynolds
Meagan Tomlin
Alain Bloom
Wayne Bonkosky
Susan Branford
Alan Coulson
Sandy Farkas
Debbie Granat
John R Kolsrud
Susan Lombard
June Michaels
Rodney Mintonye
Ben Pietsch
Dennis Hale
Don & Wanda Richardson
Will Rupe
Joanne Soracco
P. McCoy
Rex Thomas
Sally Wolfe


Newsletter Editor Needed

Fellow Rockhounds - after 3 years I'm giving up my post as newsletter editor. As my life is changing directions I need to shift my focus and attention towards other things. I will still be part of the club & continue with the website so no worries there.

This is a GREAT opportunity for someone else to add their own creative flair and knowlege to the group. The person wishing to take over this position can either keep the same format or create their own. The newsletter can be done in Acrobat Reader (and saved as a PDF) or if the person is experienced with HTML can code it right into the site as I have done.

I have several articles as well as archives from past years to pull from. Please do not feel that you must be an expert on Minerals or Geology, it may seem a bit intimidating but it honeslty is not. When I was approached to do it, I informed the entire group; I know NOTHING about rocks - I can tell you the color and that it is pretty.. that is all. And that was the honest truth!

Three years later, I have learned so much from both research, asking questions and putting the newsletter together. Thank you all for reading!!
~*~Kendra~*~

Dec. Pot Luck Party
Kick off the holidays by joining us on Dec 1st at 6:30pm for our annual pot luck party & white elephant game! Bring yourself, bring a guest & bring some food to share. We will be raffling off a beautiful piece of Lapis just over 1.5lbs. Tickets are $3 each or 2 for $5. We will also be having a door prize and Jolene is planning on BBQ'in!!

To participate in the White Elephant game, you must bring a wrapped rock (or mineral) valued under $10. Hope to see you there!!


Dec Field Trip

Gold Panning at Jim's Claim!! A lil rain never hurts who's panning for gold!! Kevin is putting together a trip during the month of December. This is a great opportunity to learn to pan and find some color. 4WD recommended. There are several nice large rocks in the creek to take home - petrified wood, japsers, bedrock.. all cool stuff!!


Return of Rock-0

UPDATE: Jan Date changed due to conflict in scheduling. STAY TUNED.

6:30pm at Round Table Pizza on Occidental Rd. Cards are $1 each. Bring the family and have some fun!! It's Bingo but with ROCKS!

In The News...
Enormous Ice Age bison skull found
Nov 9, 2010
http://www.krqe.com/dpps/news/strange/enormous-ice-age-bison-skull-found-ob10-jgr_3642942

SNOWMASS VILLAGE, Colo. (AP) - The skull of an Ice Age bison twice the size of modern bison is the latest fossil discovery coming out of Snowmass Village.

Scientists uncovered the 250-pound bison skull Saturday. The Denver Museum of Nature & Science, which is overseeing the excavation, says that when both horns were repositioned with the skull, the span of the horns was more than 6 feet.

Earlier bison specimens found at the fossil dig were smaller. Scientists have also found a Columbian mammoth, American mastodon and an Ice Age deer. The bones were first discovered last month by a construction crew.

SRGMS Newsletter Continued
Class Schedule
You do not need to be a SRMGS member to sign up for classes.
Fees are based upon $10/hr instruction.
30% of all class fees are turned over to SRMGS.

Coming Soon! Opal Cutting Class! Class size is limited.


Field Trip
We have planned a variety of trips that range from hiking difficulty
1 (low) to 5 (high).

Next trip
December Gold Panning - TBA
Location: Jim's Gold Claim
Meet: Please contact Kevin if you are interested in going. He will give more details at the Dec Christmas Party.

Goal: Pretty Pebbles, Enjoyable Day & Photos of the Harvest / Blue Moon over the city.

Difficulty level: We suggest the following: 4WD or hitch a ride from the main road to the claim with a club member. Change of Clothes, rain boots (or those sexy rubber fishing pants), bucket, shovel, warm cap for your head, food, water.. all the fun stuff.

For insurance reasons - you MUST have your dues current to attend.






SRMGS WORKSHOP LOCATION
5690 C Old Redwood Hwy
Santa Rosa, CA 95403
(707) 528-7610


Upcoming Gem and Mineral Shows
Shows located within a 3 hour drive
For a complete list see our website under FUN

October 2 & 3, 2010, Oroville, CA
Feather River Lapidary & Mineral Society
Oroville Municipal Auditorium
1200 Meyers St
Sat: 10-5 Sun 10-5


October 3, 2010, Fallbrook, CA
Fallbrook Gem & Mineral Society
Fallbrook G & M Facility
123 W. Alvarado St
Hours: 10-4


October 16 & 17 2010, Santa Rosa, CA
Santa Rosa Mineral & Gem Society
Santa Rosa Veteran's Memorial Hall
(across the street from Fairgrounds)
1351 Maple Avenue, Santa Rosa, CA
Hours: Saturday 9-6 Sunday 9-5


October 23-24 2010, Los Altos, CA
Peninsula Gem & Geology Society
Los Altos Youth Center
1 North San Antonio Road
Hours: 10-5 both days




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