MIDS Element - 14. Mass

[hardistyar]

MIDS information element	Mass
Definition	The quantity of matter in a specimen, particularly for minerals, phases and meteorites
Purpose	For many geological collections the mass of the specimen has been used as an identifier for the specimen.
Mapping
Applicable standard(s)/recommendation(s)
Element identifier
Required	Yes (Geological & Palaeontological)
Repeatable	Yes
Constraints
Examples	To be added
Element specification status	under discussion
Notes	none

Classifications of meteorites use mass to distinguish one specimen from another; in addition to registration name, year found and country (where found).

Nomenclatural code for meteorites. For examples, Meteoritical Bulletin Database.

A Mass information element should be added at MIDS level 1, and possibly also at MIDS level 0.

Information element needs to be conditionally present i.e., if material is meteorite the mass data must be present.

A similar principle also applies for crystal minerals (gem stones). Commission on new minerals, nomenclature and classification.

Source: CETAF Digitization Working Group, 7th December 2020.

[emhaston]

Whilst this information is critical for the earth sciences, it is potentially more appropriate for either MIDS-2 or MIDS-3, with the use of a specimen identifier at MIDS-0 and MIDS-1? I've therefore modified the labels for this element.

[ben-norton]

I know this may sound a little hypercritical, but the phrase should always be minerals or phases (if you get supertechnical). Gemstone names are recognizable by the public but are purely aesthetic. Mass is very important. I recommend MIDS-1. Meteorites should always include the name at MIDS-0. Every meteorite has a name regardless of when or where it was collected.

[samleeflang]

Can anyone help me with the mapping for this term? I am looking through the Darwin Core and ABCDEFG Terms but I can't find terms which directly match. ABCDEFG has UnitWeight however this is a free text field. It indicates that "details should be entered under MeasurementOrFact complex type". Is this how it is generally stored, in the MeasurementOrFact field? If anyone has an example that would be very helpful.

[tucotuco]

In Darwin Core the two options are dynamicProperties and a MeasurementOrFact record.

[samleeflang]

Thanks John! That is a very quick response

[wouteraddink]

I think specific gravity is what is ment, not total mass. Mindat stores physical properties (such as specific gravity, hardness, lustre) and chemical formula for minerals. Rocks are classified with a taxonomy that is validated by presence of certain minerals (with their CNMMN/CNMNC approved chemical formula). iSamples also does not use mass. I am not sure how important specific gravity is. I think the mineral and rock classifications are more important. the mineral names are approved by International Mineralogical Association, see: http://cnmnc.units.it/ unfortunately the list is a pdf, not the best format for sharing data.

so I think the MIDS group should reconsider the use of mass for MIDS2 and perhaps replace it by mineral name and CNMMN/CNMNC approved formula for minerals. I do not know where the rock classification that mindat is using orginates from, I think it may be the same as https://www.bgs.ac.uk/technologies/bgs-rock-classification-scheme/

Interestingly minerals and rocks have types and the types also have a type locality (which biological specimens do not have).

Kind regards, Wouter

On Mon, 6 Mar 2023 at 11:31, Sam Leeflang @.***> wrote:

Thanks John! That is a very quick response

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[ben-norton]

is generally correct. An full explanation would take 30 minutes. I'll try to keep it brief. Minerals. Minerals are classified using 3 major classification systems, referred to as Dana, Nickel-Strunz, and the IMA. The first two are more legacy than modern classifications, but used widely. IMA is the official body that determines whether a mineral is a mineral. It uses an adjusted hierarchy that stems from the original work by Nickel-Strunz. The issue is that unless someone did chemistry analysis on a given mineral, its hard to make a determination which specific name should be assigned to a mineral. In these cases, the higher group is used. Then there are gemstone names and varieties (Amethyst is just quartz that's purple). Here's an example: Olivine is not a recognized mineral name by the IMA. Its a group of minerals consisting of a couple species, but lets keep this simple. Olivine is either Forsterite or Fayalite depending on the ratio of Mg to Fe. If Mg > Fe then its Forsterite. If Fe > Mg then its Fayalite. Without context, its not possible to make this distinction from a hand sample. Therefore, its labeled Olivine.

In terms of specific gravity, its an identifying characteristic of a mineral along with habit, cleavage, hardness, luster, streak, etc. Its different than mass. Specific gravity is related to the atomic weight of cations whereas mass varies from object to object regardless of the mineral name. Since Specific gravity is related to chemistry, it remains fairly consistent among all objects that belong to a specific species. The scope of a physical property varies from a global (varies between individual objects regardless of classification) to properties indicative of a particular mineral species (shared among all objects of the same mineral name). In EFG, all physical properties are stored in a abcd:MeasurementOrFact object under the parent container MineralMeasurementsOrFacts complex type (array) with the exception of color and habit.

Rock types. Rock classification schemes are generally all based on chemistry. Without chemical analysis, its even hard to discern the validity of a specific type assignment. There are different classification systems for different rock types. BGS is the only comprehensive rock classification system for all rock types published on the web. MinDat doesn't enforce a classification system or hierarchy like a linnaean class > family > genus and species. Most collections use the same general naming system but not a strict hierarchy. Also one object may have 5 minerals and 1 rock. Its complicated. In a new model being developed, any object in a geological 'themed' collection (petrology, mineralogy, geology, so on) must have 1 mineral or 1 rock, but they may have any combination thereafter (e.g., 3 minerals and 1 rock, 2 minerals, or 1 rock are all valid). I suggest requiring at least one mineral name or rock type for level 1 or 2. I'd avoid requiring any specific physical property for level 2 or even 3.

I suggest not requiring a physical property (with the exception of maybe color) at level 1 or 2. I do recommend either 1 mineral name or 1 rock type at level 1 or 2.

[smrgeoinfo]

Back to the question whether mass should included as a level 1 property of a specimen-- for specimens that do not change mass over time (e.g. by drying out, reacting with the atmosphere, decaying, etc.) the mass of the specimen can be a useful characterization to help identify the specimen. Rock and mineral specimens are a good example, but there are other kinds of specimens for which mass would be a useful property to record.

[smrgeoinfo]

As far as rock and mineral classification, there are lots of different answers depending on what the purpose of including the 'material type' is in the specimen description. I'd suggest that a soft type approach, something like what dataCite does with subject keywords is a solution. A subject term (in this case the label for a material type) has attributes-- schemeName, scheme URI, a URI for the term, and a classification code. The you can assign the specimen to material type using different classification schemes and be clear.

[smrgeoinfo]

for some lithology vocabularies see https://github.com/smrgeoinfo/vocabulary/tree/main/lithology

[emhaston]

It's great to get the discussion on this. One point that we probably need to make super clear in the MIDS specification is that the inclusion of data in MIDS 1 is not about the importance of the data, but about the data capture processes in the mass digitisation programmes.

Am I right in thinking that this term should be replaced by Specific Gravity? I'm not seeing either term in GeoCASE.

Thanks, Elspeth

[ben-norton]

It should be mass. You often see the term weight used instead, but I think that's flawed.

[ben-norton]

It's unitWeight in efg. I understand the logic of using weight, especially from an interoperability perspective. However, I think mass is the proper measurement. Weight is a function of gravity. Mass doesn't change. It is neither destroyed nor created. Plus, there is far less consistency in the units of measurement used for weight compared to measurements of mass.

[samleeflang]

Thanks, Ben, we will include this in the MIDS calculation. Although I haven't seen this information in any of the datasets I have looked at so far. I think that is also why GeoCASE isn't showing it as it is not generally available information. It also worries me that this is a free text field in EFG extension. If this should be generally available information I think we should see if we can at least split the value and the unit, as is done in the dwc MeasurementOrFact.

[wouteraddink]

Are there any collection datasets available that actually include mass, so we can have some examples?

[ben-norton]

Are there any collection datasets available that actually include mass, so we can have some examples?

@wouteraddink Our meteorite and geology databases have both. It's just a number. Values are always in grams. I don't think a unit of measurement field is necessary in this specific case. It's all metric. With that said, you could argue its important to assure consistency, but in practical terms probably unnessecary.

@samleeflang I agree with the hesitation regarding the usage of a text field. If strings are allowed in fields containing measurements, they are no longer quantitative. Maybe it's a text to satisfy practical considerations, but that's a heavy tradeoff. Values are probably in pounds and grams.

[PipBrewer]

Mass is rarely recorded for palaeontological specimens and is not a required characteristic. I checked with curators at the Natural History Museum (London), National Museums Scotland and Natural History Museum (Denmark) about mineral and rock collections. Mass is rarely recorded for rock specimens and some mineral collections. The overall feeling is that it is not something that would be critical at MIDS2 level (although I am still following up with someone on this). However, mass is important for gem and meteorite specimens and for these specific collections it should be MIDS level 2 as it is used to distinguish between specimens. Note, it is mass, not specific gravity which is important (the latter is a property of the mineral species, not the specimen). The mineral extension for DarwinCore is being worked on and it is likely that mass will be incorporated into this, especially as it is hard to incorporate the relevant terms into the ABCDEFG schema. The Geology extension for Specify collection management system is also a couple of years from completion. Together these mean that in practice, whilst mass is an important characteristic for gems and meteorites, most collection portals will not display these details for a while yet.

[emhaston]

The decision (13 Jul 2023) based on all the discussion to date is to move this to MIDS Level 3.

Mapping is a question - DWC MeasurementOrFact?