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March 2013 Pretoria Rockhound Digest Pretoria Gem and Mineral Club Clubhouse: P.O. Box 36 888 No. 29, 26th Street, Menlo Park, Pretoria Menlo Park 0102 Tel. 012 – 460 1494 (only Sat. 11:00 – 15:00) South Africa website: www.pgmc.co.za

Chairman: Lex Krabbendam, 083 449 6812 Treasurer: Jeanne Wentzel, 082 449 5450 [email protected] Secretary: t.b.a. Vice-Chairman: Guido de Beer, Editor : Heidi Naudé, 072 923 2180 [email protected] [email protected]

Programme Highlights March 2013

*** Swop & Sell and Social 2 Mar. *** Silversmithing Course 16 Mar.

*** Gemboree 2013, Lesotho 29 Mar. – 1 Apr.

Images of Lesotho (left to right) – Maluti Mountains, Lesotho Agates, Aloes Guesthouse, Lesotho Quartz Crystals, Katse Dam, Basotho wrapped in traditional blanket on horse (Google: Images of Lesotho)

The opinions expressed in this newsletter do not necessarily reflect those of the PGMC Committee. This newsletter is the property of the Pretoria Gem and Mineral Club; articles may not be re-produced without the written permission of the Editor.

Affiliated to the Federation of Southern African Gem and Mineralogical Societies

Pretoria Gem and Mineral Club

http://www.pgmc.co.za/

PGMC Programme for March 2013: (as at 25.02.2013)

Date Event Time Contact Details

2 Mar. Swop & Sell and Social

Lapidary and Silversmithing Workshops open 11.00 – 15.00

Duty Members

7 Mar. Silversmithing Workshop open 18:00 – 21:00 Bernard Strydom, 078 187 3267 Lex Krabbendam, 083 449 6812

9 Mar. Committee Meeting

Lapidary and Silversmithing Workshops open

15.30 – 17.00

11:00 – 15:00

Committee

Please note: Open Day – Rob Smith, African Gems and Minerals – postponed, new date will be advised as soon as possible !


16 Mar. Silversmithing Course – booking essential!

Lapidary and Silversmithing Workshops open

10:00 – 15:30

11.00 – 15.00

Bernard Strydom, 078 187 3267

Duty Members


23 Mar. Lapidary and Silversmithing Workshop open 11:00 – 15:00 Duty Members

29 Mar. - 1 Apr.

Gemboree, Lesotho Weekend Gemboree Committee www.pgmc.co.za

30 Mar. Clubhouse closed – Easter Weekend

"Master Helmut Schönberger has done it again! In his Eighties and still knocking us out!”

This is a Namibian Cerussite, cut by Helmut recently. It took about a week to cut and polish - Cerussite is notoriously difficult to work with, mainly because it is extremely sensitive to temperature changes. This type of stone cracks at almost any handling, but this one decided to "play along" with Helmut's gentle touch.

The final weight was: 170.70 cts, diameter 27mm. A search on Google would appear to show this stone as coming close to second largest Cerussite ever cut - the largest being around 800 cts and kept in a Toronto museum.

The brilliant design used, comprised of 112 facets - with the large 17mm table taking a day on its own to polish. The cut produced very good brilliance.

The hardness of Cerussite is 3 - 3.5 on the Moh’s scale; it is bi-refractive with an index of 1.8 - 2.0. As with all stones, not all cuts work on all stones just because they have a certain refractive index and the cutter has to assess each stone carefully to get a good "return".

Helmut used a variety of wax laps for the polish, many of which were not working initially, but he carried on trying until one did finally work - it's the old story with gems - we know! Cerussite contains high amounts of lead which contributes to the brittle nature of the stone.

Well done Helmut - all strength to you and your great talent. Fay Pierides

http://www.pgmc.co.za/

1. Duty Roster – March and April 2013

March 2 9 16 23 30

Open – 11:00 am Will Bernard Bernard Will Closed

Duty Team Will v/d Berg Marion Blair

Nico Roux Fay Pierides

Nick Raftopoulus Zelda Carey

Will v/d Berg Jean Snyman

Easter W/E

Close – 15:00 pm Will Committee Bernard Will Closed

April 6 13 20 27

Open – 11:00 am Dieter Bernard Bernard t.b.a.

Duty Team Dieter Heinichen Linda Stone

Barry Vermeulen Gloria Schulenburg

Stella-M. Laredo Jean Schutz

Willem Vorster Marion Blair

Close – 15:00 pm Dieter Committee Bernard t.b.a.

Please note that this is the new Duty Roster starting from March 2013, please ignore the information distributed in the February newsletter. Adjustments were made already to accommodate members not able to do duty in March. The new roster will be distributed to all members who volunteered for duty shifts. Please check the dates assigned to you and organize “stand-ins” for the date/s you are not available. Please forward confirmed changes to Lex Krabbendam.

2. Membership Fees

Membership fees for 2013 are now overdue; payment can be made at the clubhouse or directly into the club’s account at ABSA Bank, branch code 335 345, acc.no. 405 584 9839. Please put your name as reference, to ensure the correct allocation of the payment. The fees for 2013 are as follows:

R 420 Principal Members

R 380 Pensioners (over 60’s)

R 60 per additional Family Member

R 30 Joining Fee (new members only)

3. Swop & Sell and Social

The Swop and Sell will be held from 11.00 onwards. Members are invited to bring their friends and family and introduce them to the club and it’s activities.

Do you have any surplus material lying around at home? Why not bring it to the club and sell it to your fellow rockhounds? Tables are supplied by the club. Dealers are also very welcome to sell their stock on this day.

After the activities we will light the fires and have the monthly bring-and-braai and socializing.

Please note:

The “Open Day” at African Gems and Minerals (Rob Smith), previously planned for 10.03.2013, has been postponed until further notice.

Rob and his team will let us know the new date as soon as possible.

1. Silversmithing Course

The next course is scheduled for 16 March at the clubhouse. Please contact Bernard Strydom or Tobias Beyers regarding the course subject, course fee and material required. Please remember that you need to book in advance for each course with them.

Bench Tips for Jewelry making - Brad Smith, California USA

BEZEL CLOSER

A bezel closer is a steel punch that makes quick work out of pushing the metal down over a round stone and burnishing it. The working end is a concave cavity that fits over your bezel or prong setting and is pushed and twisted to capture the stone. Sets can be purchased but are expensive and contain many sizes you will probably never use. If all you need is one or two sizes, here's how you can make them yourself.

Find a good quality, round steel rod a little larger in diameter than your bezel cup or prong setting. Cut a 5 inch length. File both ends flat. Locate the center of one end, center-punch a divot, and drill a small pilot hole about 5 mm deep. Remember to use a little oil as lubricant when cutting steel.

Select a ball bur a bit smaller than the steel rod but slightly larger than the bezel. Enlarge the pilot hole to a full hemispherical cavity. Test for proper fit with your bezel. Bezel should first contact the cavity about a third of the way in. When the size is correct, polish the cavity using Zam on a length of chopstick in your flex shaft. If the tool is not polished, it will leave scratches on your bezel or prongs.

When using the tool, the first step is to capture the stone correctly. I usually work by hand and push the punch straight down over the bezel or prongs. This causes the metal to start bending over the stone. Now inspect with a lens to be sure the stone is staying level. This is repeated until the stone is seated on its bearing and can't move anymore.

Next, you want to force the metal down onto the stone uniformly all the way around. While this can be done by hand, I often gently tap the punch with a hammer. Finally, I burnish the bezel by twisting the punch around.

Photo left and Diagram (middle) – courtesy of Brad Smith

See more Bench Tips at www.facebook.com/BenchTips/ or get the book “Bench Tips for Jewelry Making” by Brad Smith on Amazon

2. Faceting Classes

Members interested in faceting classes may contact Guido de Beer (tel. 083 543 4638) or Helmut Schönberger (tel. 084 620 0270), until Philip Alp is well enough to continue this task.

http://www.facebook.com/BenchTips/http://www.facebook.com/BenchTips/

3. Gemboree 2013

We have reached the last stage of the final preparations for the Pitseng Gemboree. It has been an exiting experience for your Gemboree Committee. You can find all the latest about the organized events and activities on the PGMC website. Go to: www.pgmc.co.za. and click Gemboree.

You will of course not see everything there; we kept the best for the coming Easter weekend. For those of you, who have for one of other reason not responded or need to still resolve the household budget before a commitment, please send us a provisional booking as soon as possible so that we can inform the resort about our final requirements for the Gemboree. All the necessary forms to register can be obtained from the website. Pitseng is waiting for all of us.

4. SAGCC (South African Gem Cutting Challenge) – Fay Pierides

Winning entries of the competition in November 2012 (this time with the photos provided by Fay): Faceting (photo left): Gold medal - Roy Brain, Durban Silver medal - Martine van der Westhuizen, Cape Town Bronze medal - José Portero, Pretoria Cabochons- Division A: Gold medal - Derek Scotney, Port Elizabeth (photo right) Silver medal - Colin Towers, Port Elizabeth Bronze medal - Rob Morgan, Durban

Mohs’ Scale Mohs’ scale of hardness was developed by Friedrich Mohs (1773 – 1839) and measures the hardness of “rock” on a scale of 1 to 10. The scale is not a linear scale, but somewhat arbitrary, and is based on ten minerals that were common or readily available at the time.

1 = talc, 2 = gypsum, 3 = calcite, 4 = fluorite, 5 = apatite, 6 = orthoclase, 7 = quartz, 8 = topaz, 9 = corundum, 10 = diamond

No. 10 on the scale (diamond) is 140 times harder then no. 9 (corundum), whereas no. 4 (fluorite) is only 1.11 times harder than no. 3 (calcite). A proportional measurement, called absolute hardness, was more recently devised, but is only used by scientists who need accurate results. The Mohs’ scale still satisfies all mineral collectors. Hardness is defined by how well substance will resist scratching by another substance. For example, if mineral A scratches mineral B and mineral B does not scratch mineral A, then mineral A is harder than mineral B. If mineral A and B both scratch each other, then their hardness is equal or very similar.

Source: www.deepakgems.com

http://www.pgmc.co.za/http://www.deepakgems.com/

We have not yet received the full outing report on Groot Marico, however the SA Micromounting Society kindly granted us permission to reprint the report of Stephen Gomersall. The article appeared in their recent February newsletter.

Witkop Fluorspar Mine - 02.02.2013 (by Stephen Gomersall, photos Alison Rose)

Location: Witkop mine is located 18 km south of Zeerust in the Marico district, North West Province. Products: Fluorspar Mining method: Open cast.

Geology: The Witkop fluorspar mineral deposit lies within the Marico Fluorspar Field, an area of expansive outcropping and sub-cropping of low to medium grade fluorspar in dolomite. The bulk of the fluorspar mineralisation occurs as a number of discontinuous zones in the Frisco Formation of the Malmani sub-group of the Transvaal Sequence. The predominant host rock for most of the ore is a grey, medium-grained, sparry dolomite. Courtesy Carla Thomaz, Engineering News 19th January 2007.

Six SAMS members attended, myself, Alison and Schalk. Wolf, Hennie and Johan met up with us on site whilst they were touring around the area. This year Linda had an early departure time from Hannes Palm’s farm at 08h00 which meant we had to leave Krugersdorp at 05h00.

By the time we met Wolf, Hennie and Johan at the gate to the mine they had already collected some material on the side of the road in typical rock hound fashion. The material we found was Pyrite, Tremolite Needle Crystals, Calcite, Stromabalyte, Manganese Oxide, Goethite, Hematite, Sphalerite and Galena. Our guide for the day was Koena Leso and credit goes to him for getting us to the sites we wanted to visit and trying to interpret where I thought the “A site for micro’s” was (which we eventually found after a bit of bundu bashing, turning at the right tree and going past the correct herd of Kudu .

Report shortened by the editor; members interested in the full report may contact me at heidi.naude@za. bosch.com and I will forward the whole SAMS newsletter to them.

The opinions expressed in this newsletter do not necessarily reflect those of the PGMC Committee. This newsletter is the property of the Pretoria Gem and Mineral Club; articles may not be re-produced without the written permission of the Editor.

mailto:heidi.naude@za

March 2013 Pretoria Rockhound DigestPretoria Gem and Mineral ClubPage 2Contact DetailsBernard Strydom, 078 187 3267Lex Krabbendam, 083 449 6812CommitteeBernard Strydom, 078 187 3267Lex Krabbendam, 083 449 6812Bernard Strydom, 078 187 3267Lex Krabbendam, 083 449 6812Duty Members Gemboree Committeewww.pgmc.co.za

DatePlease note: Open Day – Rob Smith, African Gems and Minerals – postponed, new datewill be advised as soon as possible !Page 3Page 4Page 5Page 6

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