[meteorite-list] Micromounts and weights - Standards Vary

From: Michael Blood <mlblood_at_meteoritecentral.com>
Date: Fri, 01 Jul 2011 14:02:36 -0700
Message-ID: <CA3383FC.1B6FF%mlblood_at_cox.net>

Mike,
        I checked this out and was confused. The first statement:
" METTLER TOLEDO AT261 0.01mg Counting Scale in HardCase"
Implies accuracy down to a tenth of one mg! That is .0001g
HOWEVER, the first part of the description reads:
Weighing Capacity:205g Repeatability:(0-50g)+/-0.015mg
Linearity:(10g)+/-0.03mg Stabilization:(typical)8-12sec
        What the h*** does that mean? It sounds like a maximum
Capacity of 205g, but "repeatability:(0-50g)+/- 0.015" seams
Like it is saying it can be off by 15mg!
        THEN: "Linearity:(10)+/- 0.03mg Stabilization..." sounds
Like they are saying it could be off by 30mg.
        How do others read this?
        Michael

On 6/30/11 5:11 PM, "Met. Mike Bandli" <fuzzfoot at comcast.net> wrote:

> Yes, and for those serious about weights, I would highly recommend a
> refurbished Mettler unit similar to this one:
>
> http://tinyurl.com/3dz8udc
>
>
> ----------------------------------------------
> Mike Bandli
> Historic Meteorites
> www.HistoricMeteorites.com
> and join us on Facebook:
> www.facebook.com/Meteorites1
> IMCA #5765
> -----------------------------------------------
>
>
> -----Original Message-----
> From: Michael Farmer [mailto:mike at meteoriteguy.com]
> Sent: Thursday, June 30, 2011 4:55 PM
> To: Mike Bandli
> Cc: Michael Gilmer; Meteorite List
> Subject: Re: [meteorite-list] Micromounts and weights - Standards Vary
>
> I use a multi-thousand dollar scale, you are right about the cheap scales,
> have bought several for the field, they are worthless.
> Wanna sell the small stuff, make the investment to do it right.
>
> Michael Farmer
>
> Sent from my iPad
>
> On Jun 30, 2011, at 4:52 PM, "Mike Bandli" <fuzzfoot at comcast.net> wrote:
>
>> 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:
>> www.facebook.com/Meteorites1
>> IMCA #5765
>> -----------------------------------------------
>>
>>
>>
>> -----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
>>
>> --
>>
> ----------------------------------------------------------------------------
>> -----
>> Galactic Stone & Ironworks - Meteorites & Amber (Michael Gilmer)
>>
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>>
> ----------------------------------------------------------------------------
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Received on Fri 01 Jul 2011 05:02:36 PM PDT