Talk:Biotite

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As mentioned in the headlining message on the page, someone needs to insert inline citations

And can we get ride of the 3rd citation? Thats a CHILD website... with no credentials to boast. I would like to see more appropriate citations from Encyclopaedia Britanica etc.74.222.64.182 (talk) 03:03, 15 September 2008 (UTC)

Inexpertly, Biotite has the general chemical formula (K Al O₂) — (MO Q)₃ — W, alloying Mafic oxides, Quartz, Water, to an Orthoclase-like Potassic Aluminum Oxide. 66.235.38.214 (talk) 09:17, 20 October 2012 (UTC)

Biotite specific gravity 2.7-3.1 vs density 2.8-3.4

How did this difference come to be. True difference or different samples or methods?

I have what I believe to be generic biotite. My specific gravity measurement using water at 1 ATM and 20C gave pretty much exactly 3.33. I am not geologist, but do have a lab with very exact balances. My number is correct. How flexible are these numbers to define biotite? — Preceding unsigned comment added by 79.102.30.85 (talk) 06:58, 31 August 2015 (UTC)

Reply: Specific gravity and density are different. Density is the mass per volume, and specific gravity is the density of a sample relative to a reference sample. If the question is about the range of reported density and specific gravity measurements, it is due to the chemical heterogeneity of natural samples. Biotite is a solid solution with aluminium, iron, and magnesium end members. — Preceding unsigned comment added by 129.11.86.22 (talk) 09:27, 2 September 2015 (UTC)

Reply: as near as I can tell, density and specific gravity should be the same in this case. The reference material for specific gravity is presumably water at ~20C? I think there is some essential info missing to explain this difference, such as compositional differences between specimens used to quantify the range of values for biotite. — Preceding unsigned comment added by 37.196.59.76 (talk) 07:53, 7 December 2015 (UTC)

Specific gravity = density w/out the units as it is a ratio. The numerical value should be the same, however as biotite has a variable composition different measurements will vary. I've removed the redundant density field from the infobox. Vsmith (talk) 14:47, 7 December 2015 (UTC)

A group of minerals not a mineral

I recently reverted a change to this article by an editor who used the edit summary "Biotite is NOT a mineral!". On further investigation it's clear that the editor was basically correct. However, it has proved difficult to find a term that is used commonly in the literature to describe this situation. I have opted to use "Biotite group" as that has been used (and definitely more that "Biotite series" or "Biotite sub-group", which were the main alternatives). Also, it seems clear from scanning through recent literature that most geologists (as opposed to mineralogists) are still happily using "biotite" as if it were a valid mineral species. I've made a start at reworking the article, but I'm a little unsure about how far to go, given that the current usage is to some extent at odds with the "official" mineralogical position. Mikenorton (talk) 11:51, 29 August 2019 (UTC)

I think your choice of "group" seems sensible. I have added a bit of historical context about biotite's status change. GeoWriter (talk) 12:47, 29 August 2019 (UTC)

Thanks - that looks a lot better. Mikenorton (talk) 18:08, 31 August 2019 (UTC)

Addition of Samadi et al. 2021 reference

I reverted the addition of this paper to the article, because it was added by the first author. It's newly published, but looks interesting and relevant. I would appreciate comments from other editors on whether it should be included. Mikenorton (talk) 11:39, 12 March 2021 (UTC)

The article looks interesting and relevant, and is in a reputable peer-reviewed journal. I think it would be a fine paper to link in the article. However, not in the lead; probably the right place for it is in the Occurrences section, where we can add a paragraph on the use of biotite in some igneous and metamorphic rocks as a thermometer. I'll see what I can do about that later this weekend, if you don't get round to it first -- right now I'm deep into trying to make some kind of order out of the Selenite (mineral) article. --Kent G. Budge (talk) 16:38, 12 March 2021 (UTC)