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This list digest contains the following message subjects:

1. LapDigest News for Issue No. 46
3. RE: Hardness vs Toughness
4. RE: Hardness vs Toughness
5. RE: Polishing and Dying Geodes and Agates
6. RE: Polishing and Dying Geodes and Agates
7. RE: Polishing and Dying Geodes and Agates
8. Re: Sphere Machine
9. RE: Sphere Machine
10. BIO: Frank Goodnough


Subject: LapDigest News for Issue No. 46

The last issue of Bill Cordua's article on hardness appears
below. I said three days ago that with the third part, I
would describe several commercially available mineral
hardness testing kits. Two kits are described below.

First, Greiger's sells a basic kit. Charles Parker, who
works there, describes the kit as follows: "We have a
Hardness Test Kit. Our # J2-1 is currently $8.75 plus
shipping. It includes 9 specimens (the usual 9 defining
minerals), a streak plate and a magnet. Our minimum order
is $15 - so two people would have to order at the same
time. Shipping is $4.75."

If you haven't seen a catalog from Greigers, you may order
it through the e-mail address: <>,
or through their web site:

The kit I use is a little more sophisticated (and costly).
It is made by Mineralab (695 East 4th Avenue, Durango, CO
81303, phone 800-749-3766 for orders.) It has 4 double
ended picks (8 metal points), a 100 grit stone for
sharpening the points, a glass plate of hardness 5.5, a
streak plate, and a magnet, all contained in a wooden
case. I don't remember the price, but it was about $40,
I think.

I want to thank Bill Cordua for preparing the paper for us..
we really appreciate it, Bill


Testing the hardness of rocks is less effective
than testing the hardness of minerals. A rock is basically
a mixture of various minerals, although it can contain
non-mineral materials such as natural glass and fossils.
(Fossils aren't minerals because they are organic, while
glass isn't a mineral because it lacks an internal
crystalline structure). Let's take a granite pegmatite for
example. This might contain grains of topaz (H= 8), quartz
(H=7), feldspars (H=6) and muscovite mica (H= 2.5). You
could thus get a range of hardness depending on which
grain you tested. In a coarse grained rock, identifying
the individual minerals allows you to identify the rock.
If the rock is fine-grained, it's harder to interpret
the results.

The hardness of fine-grained rocks tends to reflect
the average hardness of the minerals in them. Shales are
made mostly of clay and tend to be soft. Limestones and
dolostones are also soft, with a hardness of 3-4. Just watch
out if quartz sand is present mixed with the carbonates!
Quartzite and chert being made mostly of quartz are both
very hard. The hardness of sandstone may be difficult to
test. If the sand grains have not been cemented well or have
been cemented by calcite, the sandstone will seem softer.
The individual quartz sand grains will still have a hardness
of 7, but the rock may crumble or disaggregate in your hand,
making it look soft. If you think it is really soft, trying
dragging the disaggregated sand grains across a piece of
glass and you'll readily see the effects. Most igneous and
metamorphic rocks contain much feldspar, quartz, pyroxenes
and amphiboles. Their hardness is thus going to be between
6 and 7. This means hardness is not a good way to distinguish
one of these rocks from another. Volcanic glass will
typically have a hardness of 5.5 - 6.0, depending on its
particular chemical composition.

The hardness or rocks and minerals is also dependent
on the degree of weathering. Weathering may convert feldspars
(H=6) to clay minerals (H = 2 -3) Even corundum (H=9) can
alter and have rims of softer minerals such as margarite
(H= 3.5-4.5 ) around it. This is why it is important to test
as fresh or unweathered a surface as you can while doing
hardness tests.

Mohs' scale has stood the test of centuries as a
useful tool for mineral identification. Its simplicity and
effectiveness will likely assure its relevance well into
the future.

Bill Cordua
University of Wisconsin-River Falls
"Speak to the Earth and it shall teach thee" - Job

non-commercial republish permission granted

Subject: RE: Hardness vs Toughness

In a message in Issue #45 , Rick Martin writes:

> Despite its awesome hardness (in some directions), diamond
> (like lots of other crystalline minerals)has several planes
> of serious weakness. You've all seen the TV commercial of
> the guy in the back seat of the luxury sedan whose heart
> nearly stops when he cleaves a big diamond. But how well
> known is the fact that there are directions on a diamond XL
> that can't be sawn even with a diamond saw? Or any other
> known means?

Any other known means? Hmm. The octahedral crystal
directions of the cleavage planes in which you can separate
a diamond in two with a sharp well delivered blow, happens
to also be the same, also mentioned direction in which a
diamond is hardest, and cannot be sawn with a diamond saw.
Sawing is a grinding operation, and happens best along the
cubic planes of the diamond (not normally visible crystal
planes on most gem grade diamonds, The cubic direction
related to the crystal axes... They do form on some
specimin grade or industrial grade stones...) in which
directions the diamond is softest, and able to be abraded
by random bits of diamonds, many of which will be, by
chance, presenting harder directions to the operation.

The octahedral planes are not only the hardest directions
in the crystal, but also the cleavage planes. It is correct
that traditional diamond saws, which use diamond grit to
grind, cannot cut these directions. However, there IS a
known method of sawing these in addition to cleaving them.
It uses a laser, and is thus not dependent any any hardness
or toughness properties of the diamond. However, while it
is possible to saw (with the laser) along these hard
octahedral planes, what is almost impossible to do well,
is to then polish those planes. ..

Peter Rowe
Graduate Gemologist, Custom Jeweler, Lapidary
and moderator of the internet newsgroup

-Noncommercial republish persmission granted-

Subject: RE: Hardness vs Toughness

To answer the question Dianne Karg asked, in Issue #44,
about examples of minerals with the same hardness but with
different toughness, I can name several I discovered by
trial and error. Agate, quartz, tiger eye, jasper and
aventurine all have a hardness of 7. But, if you tumble
all these together (as I did), the jasper disintegrates
first, then the tiger eye, then the aventurine. I started
with a lot of agate, a few pieces of jasper, 1/2 pound of
tiger eye, 1/2 pound of aventurine, and ended with a lot of
agate and about 1 oz. of tiger eye and aventurine, and no
jasper to speak of. And for some reason, quartz seems to be
just a little tougher than agate. I have to run it longer
to get out all the pits & cracks. What did I learn from
this? Tumble only one kind of rock at a time and your
results will be much more satisfying.

Jenna Ortolani

-non-commercial republish permission granted-

Subject: RE: Polishing and Dying Geodes and Agates asked: <<....I have a 14" vibrating lap
polisher for large pieces, but there must be a much faster
way to polish small geodes etc... Would anybody tell me

There used to be a sander polisher called the Bull Wheel.
I don't know if it is still made. You can get pictures
from old Lapidary Journals or Rock and Gem. If they are
no longer made you can see how to do it from the pictures.
This unit ran at higher speed and would cause fractures if
you din't watch the heat build-up. Does anyone remember
the name of the manufacturer? I thought it was a western

Steve Ramsdell

Subject: RE: Polishing and Dying Geodes and Agates

I use an 8" (rotating) flat lap machine to do all sanding
& polishing on small geodes (after they are cut of course).
I just go through the grits (diamond) like doing cabs on a
Genie, except that I change laps to change grits, rather
than just moving over to the next wheel!
-Noncommercial republish permission is granted--

Subject: RE: Polishing and Dying Geodes and Agates

Dear Hale...

Regharding the comments about dying agates..I would like to
pose the following question:


Jeff Ursillo

Subject: Re: Sphere Machine asks: <<Anyone know where I can get a set
of plans to make a home-brew sphere machine?>>

Basically, such a machine has three identical heads, each
designed to hold a motor and apply an adjustable force toward
the sphere. With most designs the heads ride on three rails
set 120 degrees apart. To set up the machine for a specific
size of sphere, the heads are moved along their rail and
clamped into position. Then a separate adjustment is made on
each head to apply a force towards the sphere. Many designs
apply this force with bungee cords, but the better designs
I've seen use spring loading.

Most machines have an adaptor on the motor's shaft that
makes it look like a 1/2 inch male pipe thread. That allows
you to use standard iron pipe fittings to make up the
grinding/polishing cups.

The real creativity and variety in machine designs seems to
be with the various Rube Goldberg mechanisms used to apply
water and grit to the sphere. But these are too difficult
to explain without pictures.

For a machine that can do small spheres (2-6 inch diameter),
one of the requirements is a set of three motors with specs
100 rpm
1/18 hp or better
continuous duty

I've found these in surplus shops for about $13 each.

Hope this helps,

- Brad <>

-Noncommercial republish permission is granted--

Subject: RE: Sphere Machine

Recently I inherited back issues of lapidary journal -
almost all issues starting in the early sixties and through
most of the 80's - takes a big chunk of a closet! In one
of the issues I was just looking through, there were
complete plans for a small to moderate (bead to about
4 inch) three-head sphere machine. Looked fairly simple
to build.

I'm sure I can't legally duplicate the plans for you,
copyrights and all, but I can probably point you in the
right direction. Email if you want more info.

Jim Schnell
Storage Technology Corporation
(303) 673-2685
(Ed. Note: The 'LJ Index 1947-91' lists a large number of
articles on sphere making, all of which are available as
reprints from LJ (see 'How to Get LJ Reprints" file in the
Archives). There are four items listed under the heading:
"Sphere Machines, How to Make" which seem especially
pertinent to the query. They are:

.. An Easy Way to Make Spheres and Eggs - 83:01:1778
.. My Work Horse Sphere Machine - 59:02:772
.. Two Useful Grit Feed Devices - 63:08:537
.. Building a Three Headed Sphere Machine -
Part 1-65:09:710; Part 2-65:10:813

Subject: BIO: Frank Goodnough


My name is Frank Goodnough; I live in north-east Ohio in a
city of about 40,000 called Massillon. It was in 1972 after
spending one day washing gravel for corundum in Franklin NC,
I was hooked on rockhounding and all phases of earth
science; joined and became active in the local gem and
mineral society; used family vacation time to visit mines,
rockhound sites and geologic phenomenon. One nice thing
about the rock hobby is that no matter where you go there
are rocks; most often they are rocks that are different from
the ones at home.

I have a number of tumblers, a 16inch slab saw and a 5 place
arbor . I use both carborundum wheels and diamond for
shaping. Cerium oxide, Linde A and tin oxide for polishing.
I do work a lot of Ohio flint; the source of which is only
a two hour drive from Massillon.

I forgot to say in my first paragraph that I am a physician
who has been retired for almost 12 years. I don't cut and
polish as I used to but I like to read and talk about all
phases of the hobby. My E-mail address is

Frank Goodnough
1220 Nancy Anna Ave. N.W.
Massillon OH 44646
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