We Dig Rocks
by Brenda Honey
I have been mucking around with a friend’s rough topaz and have done two things. One piece I left rough and gave it a light skin polish, then mounted it in a silver basket which I made. I tried to make it look like a bloke could wear it on a black leather necklace. It looks a bit blue in one photo but it’s almost clear from the top.
The other I faceted and purchased a commercial setting for it. Yet again the photos do not capture the sparkle of the gem.
Article submitted by Marie-Ann Coyle
https://www.firemountaingems.com/resources/encyclobeadia/charts/e893
There are a lot of steps to grade a gemstone. Each step of grading focuses on a different feature and has many details that create the overall grade determination. It can be difficult to understand gemstone grades without training, so with the help of the Fire Mountain Gems and Beads gemologists we’ve created a chart to help clarify the basics. Images of both emerald and lapis lazuli are shown to illustrate transparent and opaque versions of each grade. There are other factors taken into consideration when grading colored gemstones such as the quality and rarity of the material, enhancements, overall size of the stone, uniformity of shape, quality of cutting/faceting and the combination of graded features.
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.
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:
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.
A lot of members have a supply of prehnite from Wave Hill after our field trip this year. In the last few years I have seen several members attempt to facet this material. Although it is interesting as a gem it tends to be quite “milky” in appearance and therefore has little brilliance. Vikki Thomsen has been cutting some prehnite in different designs as well as various colours and I think has created a spectacular gem with the golden yellow shown here. Although the stone is golden in natural light, it also has a green tinge on the edge of the facets. Well done Vikki
!