Crystal chemical aspects of rare earth minerals

Abstract

岩石鉱物科学 43, 11 18, 2014 日本鉱物科学会賞第 回受賞者 受賞記念研究紹介 希土類鉱物の結晶化学に関する研究Crystal chemical aspects of rare earth minerals 宮脇 律郎(Ritsuro MIYAWAKI) A rare earth mineral is deˆned as a mineral containing rare earth elements (REE: Sc, Y and lanthanoids) as essential constituents. So far, more than 280 species of RE minerals, as independent species, have been described after the o‹cial IMA CNMNC approval. The chemical bonds between REE and anions possess largely ionic character and the coordination polyhedra of REE are not regular, but rather distorted, in almost all cases. The REE 3＋ ions exhibit 7 kinds of coordination number between 6 and 12, among which 8 is the most frequently observed. The coordination numbers of the larger Ce group REE 3＋ are similar to those of Ca 2＋ and Th 4＋ , and are generally higher than those of the smaller Y group REE 3＋ , which is similar to that of U 4＋ . Isomorphous substitutions are commonly observed between cations having similar ionic radii and coordination numbers. The diŠerence in the cation size between the Yand Ce group REE results in diŠerent crystal structures, when these structures consist of isolated anionic groups, such as CO [2][3]

Review paper: Exploration geophysics for intrusion‐hosted rare metals

“…For crystal chemical purposes, the REEs are assigned to two groups: the Ce group, which is also referred to as light REEs (LREEs), that includes the lanthanides from La to Eu (Fig. ), and the Y‐group (heavy REEs, HREEs) that includes Y and the lanthanides from Gd to Lu (Miyawaki and Nakai ). From an exploration and mining perspective, the division into LREEs and HREEs is slightly different with europium included in the HREEs (e.g., Avalon Rare Metals Inc. 2014, http://www.avalonraremetals.com; IAMGOLD Corporation 2012).…”

Visible and short-wave infrared reflectance spectroscopy of REE fluorocarbonates

“…The term "rare earth elements" (REE) comprises the lanthanides, commonly yttrium (Y) and sometimes scandium (Sc) due to similar chemical characteristics. Coordination states of the REE cations in the assorted mineral structures can be quite variable (e.g., Miyawaki and Nakai 1996), ranging from a reasonably symmetrical 8-coordinated site in xenotime, to britholite with two distinct sites with coordination numbers of 7 and 9, and the REE fluorocarbonates with multiple bonding anions (oxygen and fluorine) with a coordination number of 9 (6O+3F).…”

Magnesiorowlandite–(Y), Y4(Mg,Fe)(Si2O7)2F2, a new mineral in a pegmatite at Souri Valley, Komono, Mie Prefecture, central Japan

“…In the crystal structure of magnesiorowlandite-(Y), Y and lanthanoids occupy the independent 2 crystallographic sites with different coordination numbers, 8 for the Y1 and 7 for the Y2 (Table 5). The 8-coordinated polyhedra are the most common for both the larger light REE and the smaller Y as well as the heavy REE ions among the overall REE polyhedra in the crystal structures of rare earth silicates, whereas the 7-coordinated polyhedra are less frequently observed for the larger light REE ions (Miyawaki and Nakai, 1996 (Nagashima et al, 1986). Miyawaki and Nakai (1996) assumed that the crystal structure of kimuraite-(Y) would consist of a corrugated layer of 9-coordinated Ypolyhedra and CO 3 triangles.…”

“…The 8-coordinated polyhedra are the most common for both the larger light REE and the smaller Y as well as the heavy REE ions among the overall REE polyhedra in the crystal structures of rare earth silicates, whereas the 7-coordinated polyhedra are less frequently observed for the larger light REE ions (Miyawaki and Nakai, 1996 (Nagashima et al, 1986). Miyawaki and Nakai (1996) assumed that the crystal structure of kimuraite-(Y) would consist of a corrugated layer of 9-coordinated Ypolyhedra and CO 3 triangles. However, the second dominant Nd in kimuraite-(Y) suggests different crystallographic sites for Nd and Y in the crystal structure of kimuraite-(Y).…”