North Brisbane Lapidary Club

We Dig Rocks

Feldspars

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by Ray Wilson

Feldspar is the name of a large group of silicate minerals that can be found in igneous, sedimentary, or metamorphic rocks.  Feldspars are commonly used in lapidary.  The coloured varieties make great cabochons and the clear type that can be found at Hogarth’s Range (west of gold coast) or Springsure Qld. can be faceted.  Feldspar has a hardness of 6 on the Mohs scale, so not as hard as quartz or agate.

Feldspar is an important industrial mineral being used to manufacture plate glass, container glass, ceramic tiles, plastics and other products.

Anyone interested in cabbing some Spectrolite see Carol South as the club has some material for sale.

Labradorite – a variety of plagioclase Feldspar.  Named after a location in northern Canada.   Labradorite displays an iridescent optical effect (or schiller) known as labradorescence.  Most material now comes from Madagascar.

The cause of this optical phenomenon is lamellar structure (very thin plates or flakes) with light being diffracted.

Spectrolite – A variety of plagioclase Feldspar found only in Finland.  Spectrolite is a trademarked name for this material.

Spectrolite from Finland
Labradorite from Madagascar

 The difference between Labradorite and Spectrolite is mainly that the background material in Labradorite is clear or translucent while Spectrolite the background is black.  Spectrolite tends to have more vibrant colours in reds, purples, and oranges.  Labradorite is generally vivid blues and yellow/bronze colours.

Moonstone – an orthoclase Feldspar that shows a pearly sheen or schiller.  This is the basis of the name moonstone.  Its name is derived from a visual effect, sheen or schiller (adularescence), caused by light diffraction within a micro-structure consisting of regular  lamellae.

Sunstone – is a plagioclase Feldspar that has either a hematite (iron stone) or copper inclusion.  Sunstone fund in Kong Bore Northern Territory has a hematite inclusion and appears as a series of rainbow-coloured specks rather than a schiller as in Labradorite or spectrolite

Kong Bore Sunstone

One variety of sunstone also found in the Northern Territory is a very rare Rainbow Lattice Sunstone

Rainbow Lattice


Oregon Sunstone from Oregon in USA has a copper inclusion which gives the stone a coppery coloured schiller.

Oregon Sunstone

Beginners Day April 2021

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We welcome another group of very enthusiastic beginners to the club – check out the results.

A few comments from the survey on “What did you enjoy most?”

  • Finishing a custom made piece to even wear home
  • Good company while learning to work with metals. The sawing was quite enjoyable as well as the soldering
  • Everything we were shown was great
  • Ring making
  • Entire day
  • Learning a new skill in a relaxed environment
  • The ease of explanation and practical explanation
  • Learning the processes and role of each machine
  • Really hands on good learning each step with a beautiful stone to take home.
  • Approachable and passionate instructors

Beginners Day March 2021

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March saw another very successful beginners day, once again with some very promising new members.  Below are the responses from the day and photos of their work.

What did you enjoy most?

  • Everything we were shown was great
  • Good company while learning to work with metals. The sawing was quite enjoyable as well as the soldering
  • Finishing a custom made piece to even wear home

What did you enjoy least?

  • The course ending
  • Trying to get scratches out of the silver ring, but it is a good learning experience
  • What did you enjoy least?

Use one word or a short statement to describe the day

  • Great
  • Fun
  • Fascinating. Informative. Friendly. Helpful

Additional feedback

  • It would be great to learn more about the possibilities of what can be done with silversmithing at the club
  • Very comfortable environment and will feel welcome to return as soon as allowed

Flat Lap – New Equipment Available

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The engineers trust of Peter Smith, Tom Power and Barry Kirkham have been at it again and have rebuilt the old flat lap machine from a wooden framed truck tyre based machine into a new shiny stainless steel “smicko” machine.  Stainless steel has been used on all of our work surfaces now to make maintenance and cleaning easier for members.

A flat lap is available to make polished faces on larger rocks like the one shown in this photo.

Using the 150mm diamond wheels for any stone larger than about 50mm is not permitted in the club.  The reason for this is that it causes excessive wear on the diamond wheels which are expensive, and on a technical level, it is not possible to get a perfectly flat surface on a curved wheel.  The only way to achieve this is either manually on a piece of glass or using the flat lap.

There are several laps provided with the machine, but all grinding from coarse through to prepolish are achieved using a rotating steel disk to which an appropriate grade of silicon carbide grit is added.  Water is dribbled onto the disk to make a slurry and then the rock is held firmly against the steel disk with the silicon carbide being an abrasive element to the task.  As the rock face is flattened, finer and finer grades (from 80, 200, 400, 600 up to 1,200 grade) are used to get rid of all scratches and defects on the surface of the rock.  Important! Between each grade of grit the steel disk and the rock need to be thoroughly washed to remove all traces of the coarser grit.

Once grinding has been completed and everything washed thoroughly, the polishing process can be commenced. For prepolish, a copper lap is provided which should be used with 3,000 diamond paste.

To polish,  a leather faced lap  is fitted, to which a damp slurry of tin oxide is added to this lap to complete the polishing process.

Peter has provided a user manual, with which members should be familiar before using the machine.

When next in the club, have a look at this machine, adjacent to the saw room.

A big thank you to  Peter, Tom and Barry for their efforts in providing top quality machinery for club members to use.

More Pendants

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by Mary

Just playing with what I have available!  The last pendant is an amethyst cabochon.

Materials

  • Silver plate (0.8mm thick)
  • Piece of silver for bail
  • Bezel (own choice)
  • Cabochon (own choice)

Steps

  • Measure and cut piece of silver plate, file and smooth edges and corners.
  • Add some design or stamping if desired. Stamp pendant back with ‘925’.
  • Cut a strip of silver for the bail, file and smooth edges. Anneal. Fold to form bail.

 (Consider bail size and the chain width to flow through it).

  • Using flat nose pliers to flatten and close bail ends ready for soldering. Apply flux and solder pieces to bail, and apply heat/solder.
  • Position the bail onto the centre back of the pendant.  Apply flux and solder pieces. Solder applying heat to top side of pendant.
  • Wrap bezel around the cabochon, mark bezel. Check length and cut. (Allow a little extra, adjustments can be made as you fit it tightly around cabochon).
  • Match bezel ends, place solder pieces around inside of shaped bezel. Apply heat on the outside of bezel, watch it flow. Reshape bezel and fit cabochon inside it. Check height of bezel. If bezel is too high file some off the bottom.
  • Position bezel on the pendant plate, ensuring it sits flat/flush.
  • Apply flux and solder pieces to the inside of the bezel. Apply heat around the outside and watch solder flow. Check bezel has totally attached to the pendant plate.
  • Clean and polish pendant. Put cabochon into bezel, ensuring it sits in evenly.
  • Using square end pusher tool, start to fold bezel over the cabochon, start at top and bottom, then each side (NSEW) evenly. Then carefully fold remaining bezel onto cabochon. Can use a burnisher tool to ensure bezel sits firmly onto the cabochon.
  • Give final clean and polish.

Square End Pusher
Burnisher

Pendants

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by Mary Lancaster        

Looking for a different activity, I found these cabochons in my stash and decided to have a go at making a pendant (first time!). The first one was a bit of a challenge, however trial and error resulted in the above. Maybe next time I can try using silver plate for the backing.       

 

Learning to Cab

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Always good to see members trying their hand at a new skill with great results.  We recently had a Friday night work session with Thierry instructing some members new to cabbing.

Petrified Wood

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by (Woodworm) Christoph

Here are some things about petrified wood which get me excited..... well, not just wood, all permineralised plant material.

It all started in Germany where I was born in the town of Chemnitz, world famous for its Permian petrified forest and the local museum specialising in petrified wood from around the world and particularly in Permian flora.

As a child I always loved going into the Museum für Naturkunde Chemnitz. I was amazed by the fine detail of preservation right down into the cell structure. An ancient plant turned into rock. As I grew up I met a few collectors, called wood worms, and I was hooked even more. We went on field trips all over Europe and I still have a large collection over in Germany at my parents place.

Now how does petrified wood form?

Most importantly is that the wood is covered and locked away from oxygen, so it can't rot away. In many cases petrified forests are links to volcanic activity. If things go right there is an eruption, which produces mostly ash and this ash will bury the forest. Over millions of years, minerals, predominantly quartz with other trace elements and metals will slowly impregnate the cell structure turning the wood into stone. This process is still not fully resolved.

The other way is wood gets buried by sediments such as sand. The process is the same, key is the presence of enough minerals to impregnate the wood. There have been cases that animal traces such as toredo borers (known as the famous peanut wood from the Kennedy ranges) or termites with their excrements (coprolites) have left their traces.

I'm more interested from a scientific angle of what species grew at which time, and how they have evolved through the evolution.

Petrified wood can actually be found on every continent. Yes, even Antarctica which was part of the super continent Gondwana.

There are some very famous petrified forests in the world such as the one in Arizona with its beautiful red petrified wood.

Or most exciting Araucaria cones from Argentina.

There is so much unknown still and only recently I have found a species of fern? which I haven't found in the literature yet.

Australia has got a good diversity to offer from the Permian deposits in the Bowen basin to the well sought after Jurassic woods, Donpoxylon and ferns from central Queensland around Miles and Chinchilla and Lune River in Tasmania. Cretaceous peanut wood from WA and more recent tertiary opalisiert woods from Springsure. There are many more places to find it.

A good tip is the display in the Miles historical village. It houses the collection of former Norman Donpon, a mad collector which I was privileged to meet a few years ago.

Now I could go on and on about it .....

Below are a few more pieces from my collection.