Mindat Logo
bannerbannerbannerbanner
Welcome!

IMA 2010-012 = coralloite

Posted by Marco E. Ciriotti  
avatar IMA 2010-012 = coralloite
March 27, 2012 05:00AM
Reference:
▪ Callegari, A.M., Boiocchi, M., Ciriotti, M.E., Balestra, C. (2012): Coralloite, Mn2+Mn3+2(AsO4)2(OH)2•4H2O, a new mixed valence Mn hydrate arsenate: Crystal structure and relationships with bermanite and whitmoreite mineral groups. American Mineralogist, 97, 727-734.

Abstract:
Coralloite is a new mineral found at the Monte Nero Mine (Rocchetta Vara, La Spezia, Liguria, Italy) having the simplified formula Mn2+Mn23+(AsO4)2(OH)2·4H2O. It occurs as sub-millimetric lamellar cinnabar-red crystals elongated on [100] and flattened on (001), isolated or forming wisps up to 0.5–1 mm long. Associated phases are calcite, inesite, quartz, brandtite, sarkinite, and tilasite in a chert matrix.
Crystals are pleochroic, yellow along [100] and orange-red in directions normal to it. Extinction is parallel to the cleavage traces and elongation is negative. The small crystal size does not allow accurate determination of refraction indices. Crossed polar observations of crystals placed in diiodomethane (n = 1.74) suggest that the mean refractive index is close to that value.
Coralloite is triclinic, space group P1, a = 5.5828(7), b = 9.7660(13), c = 5.5455(7) Å, α = 94.467(3), β = 111.348(2), γ = 93.850(2)°, V = 279.26(6) Å3, Z = 1. The five strongest lines in the simulated powder diffraction pattern (dobs, I, hkl) are: 9.710 Å, 100.0, (01-0), 5.166 Å, 77.1, (100); 5.136 Å, 79.7, (001); 3.342 Å, 64.8, (1-2-1); 3.324 Å, 33.6, (12-1-).
The structure of coralloite (final Rall 0.044 for 3092 observed reflections) shows similarities with bermanite: Mn2+Mn23+(PO4)2(OH)2·4H2O and ercitite: Na2Mn23+(PO4)2(OH)2·4H2O. In particular, these three minerals exhibit the same structural slab formed by [[6]Mn23+([4]XO4)2(OH)2]; X = As or P. However, these structural slabs are connected by interposed layers of different polyhedra for each mineral species.
Author:

Your Email:


Subject:


Attachments:
  • Valid attachments: jpg, gif, png, pdf
  • No file can be larger than 1000 KB
  • 3 more file(s) can be attached to this message

Spam prevention:
Please, enter the code that you see below in the input field. This is for blocking bots that try to post this form automatically. If the code is hard to read, then just try to guess it right. If you enter the wrong code, a new image is created and you get another chance to enter it right.
CAPTCHA
Message:

Mineral and/or Locality  
Search Google  
Copyright © Jolyon Ralph and Ida Chau 1993-2014. Site Map. Locality, mineral & photograph data are the copyright of the individuals who submitted them. Site hosted & developed by Jolyon Ralph. Mindat.org is an online information resource dedicated to providing free mineralogical information to all. Mindat relies on the contributions of thousands of members and supporters. Mindat does not offer minerals for sale. If you would like to add information to improve the quality of our database, then click here to register.
Current server date and time: July 29, 2014 10:52:15
Mineral and Locality Search
Mineral:
and/or Locality:
Options
Fade toolbar when not in focusFix toolbar to bottom of page
Hide Social Media Links
Slideshow frame delay seconds