[meteorite-list] Micromounts and weights - Standards Vary

From: Mike Bandli <fuzzfoot_at_meteoritecentral.com>
Date: Thu, 30 Jun 2011 16:52:28 -0700
Message-ID: <4ABE0A417DCD4C49BA85034B2D8B2E43_at_Bandli1>

A little perspective on milligrams:

There are a lot of meteorite mg weights out there that not accurate. We can
thank these new, cheap Chinese digital scales that promise accuracies of +/-
1mg or less, which are a complete joke. I bought one in Tucson to test it
out against my high-end calibrated machine and it was off by about 10 mg on
average for pieces 50 to 100 mg and 5 mg on average for pieces 10 to 50 mg.
Anything fewer than 10 mg - forget about it. The calibration weights it came
with were even more laughable...

In reality, in order to be able to accurately measure mg, you need a machine
that has been recently leveled and calibrated in-situ. I have a recently
leveled/calibrated mechanical scale whose tare changes by the hour due to
changes in the weather. It even picks up the subtle vibration of the
dishwasher downstairs.

Bottom line - a $100 mg scale isn't going to get you the accuracy needed to
accurately measure true mg. Since most people can't afford the hundreds to
thousands it costs for an accurate mg scale, I don't expect most mg weights
advertised to be truly accurate. They're close...

Just my 2 mg worth (+/- 1mg)...

----------------------------------------------
Mike Bandli
Historic Meteorites
www.HistoricMeteorites.com
and join us on Facebook:
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-----Original Message-----
From: meteorite-list-bounces at meteoritecentral.com
[mailto:meteorite-list-bounces at meteoritecentral.com] On Behalf Of Michael
Gilmer
Sent: Thursday, June 30, 2011 4:17 PM
To: Meteorite List
Subject: [meteorite-list] Micromounts and weights - Standards Vary

Hi Listees and Micronauts,

There has been some discussion recently about people buying
micromounts from a vendor on eBay and not getting the weights they
were promised. I thought I would throw out some thoughts on micros,
since those are my bread and butter.

First, the definition of "micromount" is relative. There is no
set-in-stone size bracket for what defines a micromount. It seems to
me that the general consensus is that micromounts are in the 1g range
for the more common types and sub-gram in weight for the rare types.
Very rare falls or planetaries are commonly sold by the milligram.
Rockhounds tend to equate meteorite micromounts with mineral
thumbnails. But generally speaking, most micromounts on the market
today are in the sub-gram (<1g) range.

Ideally, a micromount should be visually appealing (such a well
polished, thin part slice with good surface area to weight ratio) and
big enough to identify the lithology of the type/fall, while at the
same time being cheap enough to afford on a limited budget.

The more preparation that goes into making a given micromount, the
higher the price, generally speaking. At some point, it's not
financially viable to put a lot of cutting and polishing work into
piece of common find that is only worth a buck or two a gram.
Smaller micros are difficult to work with during preparation, for
obvious reasons, so many of the micromounts seen on the market are
unpolished, rough, or broken.

What motivates a person to collect micromounts varies from person to
person, but the most commonly cited reason for buying micros is to
temporarily fill a void in a type collection. It could be a
petrologic type, a find from a given geographic area, a fall from a
specific date, etc. Often a micromount is a temporary measure until a
nicer specimen can be acquired, or until the needed finances to buy a
larger piece can be saved up. For the very rare types and
planetaries, a micromount might be the best hope for a collector on a
restricted budget.

There are a couple of schools of thought when it comes to dealing and
selling micromounts - some dealers sell specimens by weight (by
milligram, even for specks) or some dealers offer specimens by the
piece (by eye/photo). For the most part, I am of the latter school
that sells micros by the piece. That means I don't weigh each and
every micromount, unless it is a very rare and valuable meteorite such
as a planetary or historical fall. Each dealer has their own methods
for handling micromounts and we those aren't really relevant to the
discussion at hand.

When weighing micromounts, one must use an accurate scale that is
sensitive to 1 milligram - the good ones are used by diamond and gem
dealers. There are many brands of these scales which range in quality
and accuracy. When dealing with small specks that weigh a milligram
or two, the readings can vary from unit to unit when weighing the same
specimen. If a buyer pays for and is promised a micro that weighs
100mg, it better weigh 100mg and not 50mg or 80mg. Sometimes a buyer
gets an added bonus because their personal scale is more accurate than
the seller's scale and a promised 100mg micro might weigh 120mg or
150mg. If the seller is not sticking to a strict pricing scheme ($/g
or $/mg), then ultimately what matters is if the buyer is happy with
their micromount.

>From a collector's standpoint, it pays to shop around for micromounts.
 Unless it's a very rare meteorite, it's easy to find several dealers
offering similar-sized specimens for widely-varying prices. One must
also pay close attention to the reputation of the seller and the
provenance of rare specimens. Because micros tend to be small (some
are downright tiny), it would be easy for an unscrupulous seller to
misrepresent specimens as something more valuable than what they truly
are. Chances are, if you are reading this mailing list, you are one
of those people who can find a reputable source and who does their
homework before sending payments across oceans on fiber-optic cables.

My own personal meteorite collection (the pieces I keep in my cabinet
and are not traded on my website) are mostly micromounts and I keep
the majority of them stored in 1.25" gemjars with paper labels inside
the bottom, under the foam. Some people prefer membrane boxes, small
Riker boxes, or other storage and display methods, but that is the
subject of an entire debate of it's own. The most commonly-seen
container on the micromount market is the gemjar, and thus it is a
general rule of thumb that if a specimen will fit into a gemjar, then
that specimen could/should be called a "micromount".

Best micro-regards,

MikeG

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Received on Thu 30 Jun 2011 07:52:28 PM PDT