Do you know Mohs?

July 16, 2020 By Carol

by Katarina

Mohs - Carl Friedrich Christian - was an old German fella, a geologist and mineralogist. He lived some time ago (1773 – 1839). You wonder why I mention Mohs? Well, he expanded on the knowledge from Theophrastus and Pliny the Elder who determined that Diamonds where pretty hard compared with other minerals such as Quartz.

Good old Carl used the knowledge from those who came before him and it became the basis of the hardness scale he developed, today known as Mohs’ Scale of (Mineral) Hardness.

When Mohs developed his hardness scale in 1812, very little information about mineral hardness was available. He simply selected ten minerals that varied in hardness and arbitrarily placed them on an integer scale from 1 to 10. It was a relative scale in which a mineral of unknown hardness could be tested against a group of ten index minerals to see where it positioned on the scale.

You most certainly have heard talk around the club house of how hard a piece of rock / mineral / gemstone is when people want to polish them.

This hardness is actually measured by the Mohs Scale of Hardness. The scale measures the scratch resistance of minerals, how difficult it is to scratch a specific mineral. This has an impact on how difficult it is to polish one of our pieces into a beautiful cabochon or faceted stone.

The highest resistance to scratches is found on diamonds and they have been assigned the hardness 10. The least resistance to scratches is talc – it basically scratches itself – and it therefore has the hardness of 1.

The higher a mineral is on the scale, the harder it is to polish. And the reverse works of course too, the lower the ranking, the easier it is. Which of course means you could polish a low ranking mineral away to nothing in no time.

A good indicator to how hard a mineral might be is sawing a piece. The more the saw has to work, the harder it usually is.

But all in all, the scale doesn’t mean much. After all, what does it mean for example, that an Amethyst has the hardness 7 if you have nothing to compare it with? The numbers on the scale are just that, numbers.

So I have searched the net and asked my friend Google if there are any examples for the hardness. And as Google knows everything, it has delivered. The combined findings are in the table.

One of the comments that I remember is that Stones with hardness of under 4 may not polish at all or will only take a light shine. Most of the stones hobbyists polish are found in the 6 to 7 range.

As you will see in the table, many minerals don’t have a specific hardness but rather sit on a sliding scale, depending on the composition of the minerals.

And if you ever find yourself in Vienna, why not look for the memorial plaque in honour of Carl Mohs.

So You Want to….

June 19, 2020 By Carol

Buy a Head Loupe

by Ray Wilson

A magnifying head loupe is one of the most useful tools that you will buy when you commence your journey in lapidary or metalsmithing. A head loupe gives you improved vision of your work, showing up those annoying scratches that you thought were sanded out. A head loupe gives you the magnification necessary to see your work but leaves you with 2 hands free to hold and manipulate your work.

Head loupes need to be adjustable to fit different size heads and all models should come standard with this feature. The more substantial loupes will come with a knurled nut that is wound in or out to adjust the plastic head band. Some of the cheaper types will have Velcro straps that can be adjusted to the correct head size. Loupes typically will also move up and down to allow the user to lift the loupe away from the eyes when not in use. A nice feature that means you don’t have to take your loupe off of your head when not in use. Headbands can be plastic or leather covered. Leather bands are useful as a sweat band if working in the glare of strong lights or a hot soldering torch.

Loupes also come with different type of lenses and in different shapes. The more expensive varieties will have optical glass whereas the cheaper option will have acrylic lenses. Glass lenses are an advantage as they will not scratch as easy as the plastic ones.

Each manufacturer will decide what level of magnification to offer in the lens. Standard loupes will have a magnification of around 2.5X (2.5 times). With some brands, additional lenses of increased magnification are included and can be simply replaced by undoing a couple of threaded bolts. Remember that with each increasing level of magnification the focal point comes closer to your face. For example the commonly used Optivisor with a 2.5X lens has a focal length of around 200mm. A 3.5X lens has a focal length of 100mm.

Other features are also available from some manufacturers like an additional lens for one eye, effectively doubling the magnification for that lens. Often a light is also included.

Donegan Optivisor – Rio Grande

For many years the only head loupe in the market was a Donegan head loupe made in USA. These loupes are still the standard in head loupes and you will never go wrong buying a Donegan Optivisor. Recently though the weakening Australian dollar has meant that this loupe now retails for about $120 in Australia. Recently, like so many other tools, “knock offs” or copies, that are made in China, have appeared on the market. To all intents and purposes, they are an exact copy of an Optivisor in both design and functionality. In the favour of the copy is the price. These can be purchased in Australia for around $60 and come packaged with 4 different lenses. With Optivisor only 1 lens is provided but others can be purchased as required. If this is still too much for you a copy of the acrylic head loupe with Velcro straps is available for about $20.

Other models can be purchased from places like Kogan or Jaycar.

Tiltable LED Headband – Kogan LED Headband Loupe – Jaycar

Head Loupe with 4 Glass lenses – Gemcuts

A good head loupe will last a long time. I have just replaced my original Optivisor bought in 1998. After weighing up the options I went for the Chinese knock off from Gemcuts. I can’t fault it and at $60 including 4 optical glass lenses is a great option for my failing eyesight. Given that this investment will last you a long time, buy the best that you can afford at the time.

Rocks ‘n Minerals – Do you know the difference?

June 5, 2020 By Carol

by Katarina Hayston

Being a member in the lapidary club means we are dealing with a lot of hard material, namely rocks. Their beauty lies in the eye of the beholder but most of them will get prettier the more you polish them.

But do you know whether you are holding a rock, a stone or a mineral?

I considered this on one of these self-isolation days and thought that there would be a simple explanation. Sure there is, but as usual the more you look the more answers you will find.

Let us start with “stone”. The general definition says that a Stone is piece of rock, made of hard compacted minerals, weathered to a smooth finish. Of course there are other definitions for stone, but none that apply to us here.

As we find both “rock” and “mineral” in the definition we can ignore “stone” from here on in as it is only a piece of what we are looking for.

As the definition of stone tells us that “rock” is made of “minerals” we can deduce that “minerals have to be first in order to form rocks.

The definition for mineral says that it is a solid, naturally occurring inorganic substance. Diving deeper we find that a mineral is a solid formation that occurs naturally in the earth.

Furthermore, a mineral has a unique chemical composition and is defined by its crystalline structure and shape (usually, although some do not) and it is formed naturally by geological processes (Thank you Wikipedia).

They have definitive chemical makeup as they are always made up of the same materials in nearly the same proportions.

The most common mineral structure is silicate as they contain the most common elements found in the Earth’s crust: Silicon and Oxygen. Other elements such as aluminium, magnesium and such may be present in small quantities. The most common mineral know is Quartz.

Minerals are also defined through their physical properties, which most often than not are:

Crystal structure: see below
Hardness: on the Mohs scale, a ten-point scale running from the softest, talc to the hardest, diamond.
Lustre: appearance in light
Colour
Streak: colour of a mineral when it has been ground to a fine powder. Often tested by rubbing the specimen on an unglazed plate.
Cleavage: how mineral splits along various planes
Fracture: how it breaks against its natural cleavage planes
Specific gravity: density compared with water
Any other properties (this one is my favourite)

Now that we have covered the basics of minerals we can turn to rocks.

Our stone definition has already told us that minerals are needed to form rocks. But in order for minerals to become rocks they have to be occurring naturally, in a solid combination.

Rocks are naturally occurring and coherent aggregate of one or more minerals.

Rocks are commonly divided into three major classes according to the processes that resulted in their formation. These classes are

(1) Igneous rocks, which have solidified from molten material called magma. Example: Basalt, Granite

(2) Sedimentary rocks, those consisting of fragments derived from pre-existing rocks or of materials precipitated from solutions. Example: Sandstone, gypsum, Opal (a siliceous sedimentary rock)

(3) Metamorphic rocks, which have been derived from either igneous or sedimentary rocks under conditions that caused changes in mineralogical composition, texture, and internal structure. Example: Slate and some marbles

These three classes, in turn, are subdivided into numerous groups and types on the basis of various factors, the most important of which are chemical, mineralogical, and textural attributes. And rocks can also contain organic matter, whereas minerals do not.

Maybe this helps to explain the mineral & rock situation:

Elements are needed to form Minerals. Depending on the quantity of each element present, the same elements may form different minerals.

One or more minerals (in this example all three minerals are needed) form rock under certain circumstances.

Inlaying Stone

May 22, 2020 By Carol

by Peter Smith

I have been looking at the club website. I am impressed with the project’s members are doing at home. Mary’s Silver work has always been great. I would like to be that good. Carol’s locket and Ray’s casting are excellent. I have not been at the Club much since October 2018, but I am still working on projects at home. My latest endeavour is inlaying stone. The idea came from a You Tube Video (How to make a silver and turquoise inlayed ring without a lathe). Ray said I challenged him to make one, but all I said was it is easy. I didn’t mention that it is also easy to stuff up. The problems I had were crushing the stone and using too much glue. My last project was a pair of earrings and a pendent.

Amethyst

May 1, 2020 By Carol

Much of the faceted amethyst in the market is eye-clean, meaning it lacks eye-visible inclusions.

African material, especially from Zambia, can be a highly saturated raspberry colour. It tends to have more inclusions than Brazilian material. However, due to its remarkable colour, this is considered acceptable in a faceted stone. Eye-clean material of the same colour is more valuable.

Amethysts with eye-visible inclusions but attractive colour are usually cut as cabochons or fashioned into beads. Cabochons and beads that display fine colour and high clarity sell at a substantial premium.

Rarely, amethyst undergoes fracture-filling treatment of its surface-reaching fractures to improve apparent clarity.

Amethyst is cut into a variety of standard shapes and cutting styles. These include rounds, ovals, pears, emerald cuts, triangles, marquises, cushions, and others. Facet patterns include the classic triangular and kite-shaped facet arrangements called brilliant cuts, rows of concentric parallel facets called step cuts, and mixed cuts that combine both facet arrangements.

Amethyst is also a very popular gem for cutting into a variety of freeform shapes. This is done by hand or by automated cutting. These so-called fantasy or designer cuts can be mass produced or created as one-of-a-kind pieces. They sometimes display concave faceting, where normally flat facets have a concave shape. Other types of cuts and carvings are also found, including carvings of animals and other objects.

QLD - Kuridala (near Cloncurry)
Kuridala is located about 65km south of Cloncurry in North West Queensland. This is probably the most well-known location for fossickers.

QLD - Castle Mount/Amethyst Castle (near Cloncurry)
Castle Mount is about 100km south of Cloncurry in North West Queensland. Amethystine quartz is found at this area

WA - Wyloo Station
The "Great Australian Amethyst Mine" is located on Wyloo Station in WA. Permission from the owners is required before visiting this location.

NT - Central Harts Range
Excellent Amethyst crystals and sceptres can be found in the Hart's Range.

NT - Victoria River Downs Station

NSW - Corona Station (near Broken Hill)
Very nice Amethyst has come from the Corona Station near Broken Hill.

Moses described it as a symbol of the Spirit of God in the official robes of the High Priest of the Jews, and the Russian Empress Catherine the Great sent thousands of miners into the Urals to look for it. In popular belief, the amethyst offers protection against drunkenness - for the Greek words 'amethystos' mean 'not intoxicated' in translation.

It was said to protect crops against tempests and locusts, bring good fortune in war and in the hunt, drive out evil spirits and inspire the intellect.

A little study of the works of Pliny will reveal that this gemstone, if worn round the neck on a cord made from dog's hair, affords protection against snakebite.

Later, Hieronymus even reported that eagles placed an amethyst in their nest in order to protect their young from the self-same danger.

Apart from these powers, gemstone therapists say that the amethyst has a sobering and cleansing effect. Amethyst has also been said to quell excessive stomach acid and, according to Hildegard von Bingen, served to combat insect bites and beautify the skin.

But the amethyst not only had a firm niche in medicine; it was also esteemed as a stone of friendship. And since it was thought to put the wearer in a chaste frame of mind and symbolise trust and piety, the amethyst came to occupy a very prominent position in the ornaments of the Catholic clergy over the centuries. It was the stone of bishops and cardinals; we find it in prelates' crosses and in the so-called Papal Ring (Italian, 15th century) in the Jewellery Museum in Pforzheim.

In ancient times, amethyst was already being engraved and cut into sculptured forms, witness the bust of Trajan which Napoleon captured in Berlin. Amethyst quartz, banded with whitish layers, is particularly good to work with, though it is only ever either translucent or opaque or somewhere in between. In earlier times, people liked to drink wine from amethyst cups, which brings us back to the stone's protective function against alcoholism. According to the ancient Greek saga, Diana turned a nymph whom Bacchus loved into an amethyst; hence the term Bacchus stone. Anyone wishing to protect a drunkard from delirium mixed some pulverised amethyst into the person's drink.

Synthetic (laboratory-grown) amethyst is produced by a synthesis method called hydrothermal growth, which grows the crystals inside a high-pressure autoclave.
Synthetic amethyst is made to imitate the best quality amethyst. Its chemical and physical properties are the same as that of natural amethyst and it cannot be differentiated with absolute certainty without advanced gemmological testing (which is often cost-prohibitive). One test based on "Brazil law twinning" (a form of quartz twinning where right and left hand quartz structures are combined in a single crystal[15]) can be used to identify most synthetic amethyst rather easily. It is possible to synthesize twinned amethyst, but this type is not available in large quantities in the market.[6]
Single-crystal quartz is very desirable in the industry, particularly for keeping the regular vibrations necessary for quartz movements in watches and clocks, which is where a lot of synthetic quartz is used.
Treated amethyst is produced by gamma ray, X-ray or electron beam irradiation of clear quartz (rock crystal) which has been first doped with ferric impurities. Exposure to heat partially cancels the irradiation effects and amethyst generally becomes yellow or even green. Much of the citrine, cairngorm, or yellow quartz of jewellery is said to be merely "burnt amethyst"
Wiki-how – testing amethyst
And for the more scientific minded, check out the paper on GIA website

Wikipedia – http://en.wikipedia.org/wiki/Amethyst

Mindat – http://www.mindat.org/min-198.html

Minerals.Net – http://www.minerals.net/gemstone/Amethyst.aspx

Fossicking Australia – http://gemfossicking.com.au

Gem Society – https://www.gemsociety.org

GIA – https://www.gia.edu/

Show and Tell

April 24, 2020 By Carol

by Ray Wilson

After a few failed starts and modifications to equipment aided by Ray Tierney and Tom Power I have now established a home casting workshop.

I have made silicon rubber moulds, made wax patterns from the moulds, and then invested the wax models in plaster investment followed by burning out the model and using a centrifuge caster to produce sterling silver jewellery pieces – a complete end to end process.

I have also been enjoying finishing off some boulder opal pieces; some of which were cut several months ago and were put aside.

This week I am going to have another attempt at making an inlay ring – challenged by Peter Smith. The You Tube video makes it look simple, but I have discovered a few secrets to stuffing up an apparently simple process. Peter is almost at the production stage now and has made up a special “dolly pot” to crush coloured rock to make the inlay. If anyone wants to try this challenge below is the You Tube link.

Y ouTube – Inlay Ring

Polishing Rocks

March 29, 2020 By Carol

8 Expert Tips on How to Polish Rocks

1. Grind wet. Always grind wet to protect your lungs from breathing in the dust from stone polishing. The dust from some stones, such as malachite, is quite toxic. In addition, wet grinding eliminates damage to expensive diamond wheels and stone-polishing tools.

2. Judge dry. Although we always grind wet, we recommend that you always dry the stone completely before judging its surface. Water on the stone surface will only hide scratches and give a false reading.

3. Use the whole wheel. Use the entire width of the grinding wheel, not just the centre. This will ensure a longer life and better performance for your diamond wheel.

3. Use the whole wheel. Use the entire width of the grinding wheel, not just the centre. This will ensure a longer life and better performance for your diamond wheel.

4. Skip no grit. Work sequentially from the coarsest to the finest grit. Don’t be tempted to take a short cut by skipping a grit in order to save a little time. The progression through finer and finer grits is necessary to remove the scratches left by the previous grit. The goal is to have the scratches become finer with each grit size until they can no longer be seen. Our experience has been that if you skip a grit, the final polish will show big scratches.

You will wonder where those scratches just came from! The truth is that they were there all the time, but you just didn’t sand them out when you were supposed to. If you skip a grit and find deep scratches, you’ll have to go back three or four grits to remove them. It’s always faster to do it right the first time than to try to take shortcuts and risk damaging the stone you’re working on.

5. Polish slow. Polishing is the final step. There are a myriad of polish and stone-polishing pad combinations; our preference is charging a soft leather pad with a thin paste of polishing compound and water. The actual polishing occurs as the pad starts to dry and the stone starts to pull against the surface. We keep the speed of the pad low to eliminate any heat buildup.

6. Keep it clean. Remember, “Cleanliness is next to Godliness” is especially important when it comes to lapidary work. To prevent cross-contamination from coarse grits, we are careful to rinse the stone and our hands at every grit change during stone polishing. We also thoroughly clean our machines after each grinding session to prevent contamination when moving through grit levels.

7. Believe what you see. Your eyes are your most important tools when it comes to stone polishing. They are your feedback loop. If your eyes tell you that something is not quite right about the surface, believe them. Stop! Figure out what the problem is before continuing, and think through the steps you’ll take to remedy it before you begin.

8. Grind a little and look a lot. This is the mantra of the successful lapidary. Taking your time and being very observant during the polishing process is essential to secure the results you want.

Rocks, Minerals & Gems

June 4, 2018 By Katarina Hayston

Obsidian. An article on Obsidian forma and the use of this volcanic glass.
Mookaite – The stone that shines

COVID-19 Update

Until the 1.5m social distance restrictions are relaxed, unfortunately we cannot accept new members and attendance at the club by anyone is by invite/roster only.