Log InRegister
Quick Links : The Mindat ManualThe Rock H. Currier Digital LibraryMindat Newsletter [Free Download]
Home PageAbout MindatThe Mindat ManualHistory of MindatCopyright StatusWho We AreContact UsAdvertise on Mindat
Donate to MindatCorporate SponsorshipSponsor a PageSponsored PagesMindat AdvertisersAdvertise on Mindat
Learning CenterWhat is a mineral?The most common minerals on earthInformation for EducatorsMindat ArticlesThe ElementsThe Rock H. Currier Digital LibraryGeologic Time
Minerals by PropertiesMinerals by ChemistryAdvanced Locality SearchRandom MineralRandom LocalitySearch by minIDLocalities Near MeSearch ArticlesSearch GlossaryMore Search Options
Search For:
Mineral Name:
Locality Name:
Keyword(s):
 
The Mindat ManualAdd a New PhotoRate PhotosLocality Edit ReportCoordinate Completion ReportAdd Glossary Item
Mining CompaniesStatisticsUsersMineral MuseumsClubs & OrganizationsMineral Shows & EventsThe Mindat DirectoryDevice SettingsThe Mineral Quiz
Photo SearchPhoto GalleriesSearch by ColorNew Photos TodayNew Photos YesterdayMembers' Photo GalleriesPast Photo of the Day GalleryPhotography

EducationHow do rocks get named?

4th Mar 2012 14:09 UTCJason Evans

I am not sure if i understand this correctly but I think the IMA is the organization that approved mineral names, but what about rock names, is there the IMA equivalent for rocks? I would like to find out if there is an official term for the rock consisting of greyish purple opaque zoisite , Tsavorite garnet, pyrite, graphite and possibly a few more that i have not noticed. and also is there a name for the rock from Turkey that's sold as Lavender Jade?

4th Mar 2012 15:34 UTCDavid Von Bargen Manager

"is there the IMA equivalent for rocks?" - No.

4th Mar 2012 17:14 UTCMichael Kieron Expert

For igneous rocks refer to The IUGS systematics of igneous rocks, 1991, by M. J . Le Bas & A. L. Streckeisen and you'll see the ways, means, and difficulties that go behind all these.


Anyway, rock classification is based on some systematics based on mineral content and there are ternary diagrams to give a reasonable (to a geologist) name to a rock. For example cumberlandite is technically just another magnetite melatroctolite based on the ratios of olivine, plagioclase, and pyroxene along with a large amount of magnetite.


Tanzanite and tsavorite may be mineral assemblages within the rock but I would not think of them as a rock type. I have rocks from an old copper mine with chalcopyrite, bornite, molybdenite, epidote and grossular but I would still call the rock a greenschist, maybe even an epidote greenschist.


From what I know, the rocks at Merelani are mostly dolomitic marbles and graphite gneisses and I would consider tanzanite/tsavorite as minerals hosted as veins and pockets within.


-Mike

4th Mar 2012 17:51 UTCJason Evans

Thanks, OK so what defines a rock from a mineral assemblage? I though that's what a rock technically is? As the ruby/zoisite/.tschermakite mix gets its own name (Anyolite) i wonder why the purple zoisite/tsavorite mix also doesn't have its own name.

4th Mar 2012 18:57 UTCDavid Von Bargen Manager

"i wonder why the purple zoisite/tsavorite mix also doesn't have its own name." - the people selling it have a bit more sense / don't need to hype it.


There are rock names such as granite, basalt, sandstone, schist, that have been used by geologists/petrographers for a long time. With a rock, you really need to have a lot of it (enough to qualify for mapping). Gemstone names tend to be coined to help sell something, either by adding adjectives to real minerals/gemstones (smoky topaz - really just smoky quartz) or trying to give it some cachet or suck up to someone (kunzite).

4th Mar 2012 22:57 UTCJason Evans

well i think the people who do sell it are hyping it by calling the purple zoisite, Tanzanite! If it occured as gemmy well formed crystals then maybe they could get away with using Tanzanite but all the specimens i have seen just have a very ugly grey purple opaque material, and I have also notice they must be photographing it with a flash or something because that seems to make the purple colour stand out more, in both of my specimens the actual colour is nothing like how it appears in all the photo's i have seen. It must be quite rare as I have not seen many places which have it, 1 or 2 online sites and occasionally a bit appears on eBay. but with so many on line mineral sites i'm surprised there is not more available. 1 of those sites gives the locality of their specimens as near the famous scorpion mine in the taita hills in kenya, if this is true then the locality info for Tanzanite needs to be changed.

I am still curuious about what i can call my lavender jade from turkey, i have found out that the jade part of the rock is actually jadeite but i cannot call it jadeite as its only 40-50% jadeite so should i just call it a jadiete containing metamorphic rock? I'm sorry if i seem pedantic about these things but i just like to have things in my collection labeled correctly.

5th Mar 2012 01:02 UTCDon Saathoff Expert

Jason, if your "lavender jade" were in my collection I'd label it as "jadeite/(whatever the metamorphic rock is)...eg, "jadeite/schist". As far as the zoisite is concerned, regardless of what the seller calls it, it is in your collection and you can correct incorrect usages for your satisfaction but there is no way to change marketing hype but through educated buyers.....


Don

14th Apr 2012 09:19 UTCRalph S Bottrill 🌟 Manager

Its good to see people conciencious about naming rocks! Metamorphic rocks are usually described with a base name like schist, hornfels etc prefixed by mineral modifiers, in the case of this zoisite rock, probably zoisite skarn. Re the purple jadeite, it depends what else is in it and how it occurs: possibly a jadeite granulite? Or jadeite blueschist? But as Michael indicated they may just occur as veins, pods or nodules etc and thus not merit formal names.

23rd Apr 2012 03:43 UTCMarco Jamer

It depends on how they were discovered. There are some which are named from the dominant material found in them. And there are usually some which are named based on the word that describes them the most. Usually, they are quite descriptive about it and in some rare instances, the names of the those who discovered them are put to consideration. Or even where and when they are found.
 
Mineral and/or Locality  
Mindat Discussions Facebook Logo Instagram Logo Discord Logo
Mindat.org is an outreach project of the Hudson Institute of Mineralogy, a 501(c)(3) not-for-profit organization.
Copyright © mindat.org and the Hudson Institute of Mineralogy 1993-2024, except where stated. Most political location boundaries are © OpenStreetMap contributors. Mindat.org relies on the contributions of thousands of members and supporters. Founded in 2000 by Jolyon Ralph.
Privacy Policy - Terms & Conditions - Contact Us / DMCA issues - Report a bug/vulnerability Current server date and time: March 28, 2024 19:38:11
Go to top of page