Discussions

💬 Home 🔎 Search 📅 Latest

╳Discussions

💬 Home 🔎 Search 📅 Latest

Groups

Recent Images in Discussions

MineralsLiskeardite

16th Jun 2015 14:11 UTCJolyon Ralph Founder

I've heard from reliable sources that "all liskeardite from Penberthy Croft in Cornwall is probably bettertonite", It's highly likely the Wheal Carpenter material is the same, thus leaving the Marke Valley (type locality) material as the only genuine Cornish Liskeardite.

Liskeardite has suddenly become a much rarer mineral :)

All three of our head photos for Liskeardite are currently the Penberthy material, I will change it to point to the Marke Valley pieces.

16th Jun 2015 14:32 UTCTimothy Greenland

Liskeardite was already noted as: "IMA lists as Questionable" in the 2014 Fleischer... Perhaps even the type material needs confirmation?

Best wishes

Tim

16th Jun 2015 14:38 UTCReiner Mielke Expert

How was it decided that there was liskeardite at Penberthy Croft in the first place? Someone must have done XRD to confirm it?

16th Jun 2015 14:43 UTCJolyon Ralph Founder

Well, I guess that depends how old the reference is to liskeardite at the site. Analytical cornish mineralogy predates XRD by a long way

16th Jun 2015 14:59 UTCJolyon Ralph Founder

I doubt liskeardite is a questionable mineral - resarch has been done on it recently, see Grey, I.E., Mumme, W.G., MacRae, C.M., Caradoc-Davies, T., Price, J.R., Rumsey, M.S., Mills, S.J. (2013): Chiral edge-shared octahedral chains in liskeardite, [(Al,Fe)32(AsO4)18(OH)42(H2O)22]•52H2O, an open framework mineral with a pharmacoalumite-related structure. Mineralogical Magazine, 77, 3125-3135.

16th Jun 2015 15:00 UTCReiner Mielke Expert

Hello Jolyon,

I was thinking of the dealers who sold it as liskeardite, but I guess that is probably wishful thinking.

16th Jun 2015 16:38 UTCJolyon Ralph Founder

Indeed :)

16th Feb 2016 11:00 UTCUwe Kolitsch Manager

Grey, I.E., Kampf, A.R., Price, J.R. and Macrae, C.M. (2015): Bettertonite, [Al6(AsO4)3(OH)9(H2O)5]·11H2O, a new mineral from the Penberthy Croft mine, St. Hilary, Cornwall, UK, with a structure based on polyoxometalate clusters. Mineralogical Magazine 49, 1849-1858.

Bettertonite, ideally [Al6(AsO4)3(OH)9(H2O)5]·11H2O, is a new mineral from the Penberthy Croft mine, St. Hilary, Cornwall, England, UK. It occurs as tufts of white, ultrathin (sub-micrometre) rectangular laths, with lateral dimensions generally <20 μm. The laths are flattened on {010} and exhibit the forms {010}, {100} and {001}. The mineral is associated closely with arsenopyrite, chamosite, liskeardite, pharmacoalumite, pharmacosiderite and quartz. Bettertonite is translucent with a white streak and a vitreous to pearly, somewhat silky lustre. The calculated density is 2.02 g/cm3. Optically, bettertonite is biaxial positive with α = 1.511(1), β = 1.517(1), γ = 1.523(1) (in white light). The optical orientation is X = c, Y = b, Z = a. Pleochroism was not observed. Electron microprobe analyses (average of 4) with H2O calculated on structural grounds and analyses normalized to 100% gave Al2O3 = 29.5, Fe2O3 = 2.0, As2O5 = 30.1, SO3 = 1.8, Cl = 0.5, H2O = 36.2. The empirical formula, based on 9 metal atoms is Al5.86Fe0.26(AsO4)2.65(SO4)0.23(OH)9.82Cl0.13(H2O)15.5. Bettertonite is monoclinic, space group P21/c with unit-cell dimensions (100 K): a = 7.773(2), b = 26.991(5), c = 15.867(3) Å, β = 94.22(3)°. The strongest lines in the powder X-ray diffraction pattern are [d obs in Å(I) (hkl)] 13.648(100)(011); 13.505(50) (020); 7.805(50)(031); 7.461(30)(110); 5.880(20)(130); 3.589(20)(02); 2.857(14)(182). The structure of bettertonite was solved and refined to R 1 = 0.083 for 2164 observed (I > 2σ(I)) reflections to a resolution of 1 Å. Bettertonite has a heteropolyhedral layer structure, with the layers parallel to (010). The layers are strongly undulating and their stacking produces large channels along [100] that are filled with water molecules. The basic building block in the layers is a hexagonal ring of edge-shared octahedra with an AsO4 tetrahedron attached to one side of the ring by corner-sharing. These polyoxometalate clusters, of composition [AsAl6O11(OH)9(H2O)5]8–, are interconnected along [100] and [001] by corner-sharing with other AsO4 tetrahedra.

16th Feb 2016 18:32 UTCJohn Betterton

Dear Sir,

I wonder why you have underlined liskeardite on the above abstract? Liskeardite is still a valid mineral at Penberthy Croft. It has been checked by synchrotron and electron microprobe methods using my specimens along with the type specimen from Mark Valley mine by the above lead author. So please remove the ? mark from the Penberthy Croft mineral listings, it only confuses collectors.

A paper dealing with the various Al-arsenates from both locations will be written shortly this topic.

John Betterton

17th Feb 2016 19:11 UTCUwe Kolitsch Manager

> I wonder why you have underlined liskeardite on the above abstract?

To indirectly answer the question of Reiner Milke

"How was it decided that there was liskeardite at Penberthy Croft in the first place?"

> So please remove the ? mark from the Penberthy Croft mineral listings, it only confuses collectors.

I hadn't added it, but will remove it now.

19th Feb 2016 23:24 UTCJohn Betterton

Dear Sir,

Thank you for correcting the liskeardite entry. I wonder if can add the new revised list of minerals on this location. I have sent this to Jolyon but is too busy to add the data.

Penberthy Croft mine is situated approximately one mile from the village of Goldsithney in the parish of St. Hilary, Cornwall, England. NGR, SW 555 324. The locality is a prolific source of rare and unusual secondary minerals of which the Cu-Pb-Fe-Al arsenates are the best known. Penberthy Croft is the type locality for the following species: the copper lead arsenate bayldonite and the aluminium arsenates bettertonite and penberthycroftite.

Penberthy Croft is the first, or joint first recorded site for the tin hydroxide minerals jeanbandyite and natanite in the British Isles. Segnitite is also first recorded at this location.

Note on the mineral lists:

Reference to adamite at Penberthy Croft is from Kingsbury. Given the doubts about the provenance of other Kingsbury specimens (Ryback et al. 1998, 2001), investigated this and discredited the occurrence.

Should be followed by a separate list of discredited/fraudulent/unconfirmed minerals from the main list of only confirmed species:

List of confirmed mineral species supported by analytical data:

Adamite

Agardite-(Ce)

Agardite-(La)

Alloclasite

Anatase

Anglesite

Ankerite

Annabergite

Aragonite

Arsenolite

Arsenopyrite

Aurichalcite

Azurite

Bayldonite (TL)

Beaverite-(Cu)

Bettertonite (TL)

Beudantite

Birnessite

Bismuthinite

Bismutite

Bornite

Brochantite

Bulachite

Calcite

Caledonite

Carminite

Cassiterite

Cerussite

Chalcoalumite

Chalcophyllite

Chalcopyrite

Chamosite

Chrysocolla

Clinochlore

Connellite

Copper

Corkite

Cornubite

Cornwallite

Covellite

Cuprite

Cyanotrichite

Devilline

Dolomite

Duftite

Erythrite

Fluorapatite

Galena

Goethite

Gypsum

Halite

Halloysite

Hidalgoite

Jarosite

Jeanbandyite

Langite

Laurionite

Leadhillite

Libethenite

Linarite

Liskeardite

Malachite

Mansfieldite

Mattheddleite

Millerite

Mimetite

Mixite

Monazite-(La)

Natanite

Olivenite

Orthoclase

Parnauite

Penberthycroftite (TL)

Pharmacoalumite

Pharmacosiderite

Philipsburgite

Phosgenite

'Pitticite'

Plumbogummite

Pseudomalachite

Pyrite

Pyromorphite

Quartz

Redgillite

Scheelite

Schulenbergite

Scorodite

Segnitite

Siderite

Silver

Smithsonite

Sphalerite

Stannite

Stilpnomelane

Sulphur

Tenorite

'Varlamoffite'

Woodwardite

Wroewolfeite

Wulfenite

Zincolivenite

101 mineral species are valid for this location not 115 as currently stated on the Mindat.org website. List of discredited/fraudulent/unconfirmed/to be confirmed species. (K= Kingsbury Collection at the NHM either discredited or fraudulent). Others are due to lack of analytical data:

Arseniosiderite K

Atacamite K

Beraunite discredited

Bieberite discredited

Cattiite K

Ceruleite discredited

Churchite-(Y)

'Hornblende' discredited

Lepidocrocite

Mottramite discredited

Paratacamite K

Plumbojarosite K

Rosasite K

Serpierite discredited

Tyrolite discredited

Vanadinite discredited

Wurtzite

Zálesíite discredited

Unknowns (UK PC = Unknown Penberthy Croft) from the John Betterton Collection:

UK PC2 ? MnxOx

UK PC3 ? Cu+Zn+As+Mn+Fe+Co??+La???+O

Additional work is required on these unknowns.

I have other minerals to be added when published in the mineralogical literature. By John Betterton (Museum Geologist/Mineralogist). February 2016.

21st Feb 2016 13:17 UTCKnut Edvard Larsen 🌟 Manager

Thanks John,

The locality page is updated according to your post above.

Those minerals in your list marked as " discredited" is now set as " erronously reported" in the mineral list (the mineral is crossed over with a line), and those marked K and the rest as " unconfirmed", that is the mineral with a question mark.

Comments also added on each entry with reference to your informations given above (I have not access to the articles in the UK Journal of Mines & Minerals, or else I would have entered these as reference.)

You are also welcome to add new minerals to the page, see the manual:

http://manual.mindat.org/index.php/Add_Minerals_to_a_Locality

21st Feb 2016 22:38 UTCJohn Betterton

Dear Sir,

Numerous thank for the added update. The only thing remains is that there are to date 101 valid species and the website entry now has 108 (even I added up the revised listings and also get 101, so why 108?

Best regards,

John Betterton

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: May 2, 2024 17:13:04

Go to top of page