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Faceting rough - drilling

rebecca - as a pragmatic lapidary & designer i look for the least
complicated way to attain the results i need. for drilling pieces of
quartz, the next notch down from diamond on the mohs hardness scale,
i do this:

1 - put a little water in a small shallow container (i use the
dressing or mashed potato containers that come with the thanksgiving
dinners from publix markets - hey, that’s a busy show time for me),
fold a small piece of cloth & stick it into the container to get
slightly wet -

2 - hold the stone with the folded cloth -

3 - start drilling with a small ball diamond burr. when the ball is
halfway into a hole, change to a larger ball diamond burr -

4 - every now & then dip the stone & burr into the water (if i need
to to tell you to not do this while it’s running then please stay
away from electrical equipment of any kind!) & drill some more - burr
breakage is almost always heat induced -

5 - & so on until you have the hole depth & diameter you need. it’s
impossible to drill quartz without the diamond bonded or sintered
burrs - i DO NOT want to hear from any of you who have gotten great
results using toothpicks & grains of sand, okay? you’ve got a life -
use it! ive

   quartz, the next notch down from diamond on the mohs hardness

Ive, are you being sarcastic when it comes to drilling quartz? Does
it seem almost like drilling a diamond?

If not, quartz is three notches down from diamond on Mohs’ hardness

10 - Diamond
9  - Corundum
8  - Topaz
7  - Quartz

Charles Heick

The Moh’s scale is not linear. Quartz is not three, but several
thousand notches less hard than diamond.

Hans Dursling
Moncton, Canada

All, The major problems with diamond drilling stones is control of the
drill and control of the piece to be drilled. Control of the drill
can be accomplished by purchasing expensive equipment that accurately
locks in the drill and guides it at a constant speed into a
stationary piece of stone. The drill is constantly lubricated as it
moves in and out of the stone being drilled. For those of us whom do
not have these machines here is a couple of hints that may help.

  1. Shorten the shaft of the drill. I normally cut one drill down to
    about 1/2 inch long. This is the drill I use to start the hole.
    After the hole is started I change to a regular length drill. 2.
    Start the hole using the edge of a spinning drill. The edge always
    has sharper diamond exposed and will quickly give you an area that
    you can anchor the bit into to start your straight hole. 3. Always
    start the hole with a new drill bit. 4. Whenever possible drill the
    hole before finishing the stone. 5. Make a jig to hold the stone out
    of two pieces of Plexiglas, bolts and nuts, and a hole to guide the
    drill through.

Gerry Galarneau

Gem hardness, now that’s an interesting subject. In 1822, German
mineralogist Friedrich Mohs developed the well know, but sometimes
deceptive, Mohs’ scale. A list of well-known minerals were chosen
and assigned a number in order of their relative hardness. A simple
scale to show which stones can or cannot scratch another. Therefore,
a mineral of the same number on his scale can scratch another mineral
with the same number or lower. That’s all it was intended to be.

Hans, saying Quartz is “several thousand notches less hard than
diamond” may be somewhat an exaggeration, but it does get the point
across. You are right to say Diamond is many times harder than
Quartz, which is just three notches lower than Diamond on the Mohs’
scale. However, it is still three notches lower in reference to this

To indicate hardness of a gem or mineral in a precise manner, a
Sclerometer is required. The values obtained using this instrument
shows a much truer relative hardness. As a comparison to the Mohs’
scale, the following values are obtained:

Mineral Mohs Value

Diamond - 10 - 140,000
Corundum - 9 - 1,000
Topaz - 8 - 459
Quartz - 7 - 245
Feldspar - 6 - 191
Apatite - 5 - 54
Fluorite - 4 - 37
Calcite - 3 - 15
Gypsum - 2 - 12
Talc - 1 - 1

Hardness (resistance to scratching) should not be confused with
toughness (resistance to chipping, breaking or cracking). In a
toughness contest between Diamond and Jade, Jade would win.

Charles Heick

Charles, I guess the Mohs scale is similar to the Richter Scale, where
just one point can be the difference between a roll and a catastrophe.

Charles Heick, would you please post some other numbers for relative
hardness of stones using the sclerometer ratings?

Of special interest to me personally would be numbers for spinel,
beryl, chrysoberyl, and other stones at the higher end of the scale.

If you have about relative toughness of stones and how
that is measured, it would also be useful to post that.

Ricco Gallery
125 W German St/PO Box 883
Shepherdstown WV 25443

   "...I guess the Mohs scale is similar to the Richter Scale,
where just one point can be the difference between a roll and a
catastrophe. Teresa " 

Yes and no, Teresa. Yes, one point difference on either scale means
an order of magnitude much greater than one. However, there is a
logical mathematical order to the Richter scale, while there is no
mathematical order to the Mohs scale. The Richter scale is a
logarithmic order of magnitude scale of geological forces (volcanic
and tectonic). Each one point increment is exactly ten times greater
than the preceding whole number value and about thirty times greater
in the magnitude of energy.

Now, applying this type of scale to mineral hardness, what if we took
the minerals on the Mohs’ scale and converted them to a logarithmic
scale using the values obtained from a Sclerometer. We could call
this something like the Mohs Modified Logarithmic Scale or Mohs MLS
for short. Well, lets try it:

Mohs   Mineral    Sclerometer   Mohs MLS
10  -  Diamond   -  140,000    5.146
9   -  Corundum  -    1,000    3.000
8   -  Topaz     -      459   2.662
7   -  Quartz    -      245   2.389
6   -  Feldspar  -      191    2.281
5   -  Apatite   -       54    1.732
4   -  Fluorite  -       37    1.568
3   -  Calcite   -       15    1.176
2   -  Gypsum    -       12    1.079
1   -  Talc      -        1    1.000

As you see, Diamond becomes 5.146, while the softest, Talc, stays at

  1. All but Diamond is squeezed into two whole units (1 thru 3).
    Unless you can visualize a logarithmic scale in your minds eye, is a
    logarithmic hardness scale much improvement at all? The difference
    between Diamond and Corundum may seem small at first glance, 2.146
    units. A logarithmic scale seems best left to orders of energy.

Anybody with a better idea for a hardness scale?

Charles Heick

   "...would you please post some other numbers for relative
hardness of stones using the sclerometer ratings?" 

Hello Ricco. With the Mohs’ Scale of Minerals being the accepted
standard among mineralogists and gemologists, there isn’t much
published on Sclerometer values for gem materials other than those
listed on the Mohs scale. I do not have access to a Sclerometer
myself and have only read about it.

The relative hardness of minerals found on the Mohs’ scale appears
sufficient for material identification without a need for
scientifically exact values. However, I must admit, absolute values
give us all a better understanding of exactly how hard a material is
in reference to another. But, that is the way it is and we aren’t in
a position to change almost two centuries of tradition.

In the gem world, relatively speaking, there are very few natural
gemstone materials harder than 7.5 on the Mohs’ scale. I did a
search and other than those listed on the scale itself, only found
twelve rated 7.5 and higher:

Andalusite    7.5
Beryl         7.5
Euclase       7.5
Garnet        7.25-7.5
Hambergite    7.5
Phenakite     7.5
Sillimanite   7.5
Tourmaline    7.5
Zircon        7.5
Spinel        8.0
Taaffeite     8.0
Chrysoberyl   8.5
   "If you have about relative toughness of stones and
how that is measured..." 

A gemstones toughness, along with hardness and stability, determines
its durability. Toughness is rated as either exceptional, excellent,
very good, good, fair or poor. I do not know what tests are done to
determine a stones toughness rating. I have read of the Briggs’
scale for the ranking of brittle minerals. Fragments of two
different materials are positioned on a scale and pressed against
each other until one of them breaks. The one that breaks is lower in
toughness. Sorry I couldn’t be of greater help to you.

Charles Heick

Anybody with a better idea for a hardness scale?

At the risk of sounding silly, keep the “KISS” principal (“Keep It
Simple, Stupid…”, and no, I’m not calling anyone stupid. That’s
just the accepted acronym) in mind. I see no reason why those
Sclerometer readings need to be converted to a logrithmic scale.
Sure, it makes the numbers amaller, but it also makes them harder to
interpret, less intuitive. Why not just keep the raw measurement data
as is? I see no problem in listing the hardness of diamond as Scl
(Sclerometer, or whatever shorthand notation for that instrument is
appropriate) 140,000. The more pressing question, I should think, is
to determine the best type of instrument to use to make the
measurements. hardness can be measured in a number of ways, giving
somewhat varying results. It seems to me the most important question
is to decide which means of measuring a stone’s hardness most closely
paralells the observed behavior of that stone in the uses we make of
it, so the hardness figure we state is the most accurate statement of
the stone’s hardness in real life situations.

Peter Rowe