AND

SUMMARY. A new analysis of the type material of cheralite specifies the individual rare earth elements. Unit cell contents are: (REEl.ssTh1.15Cal.03Pbo.osUo.15)3.96 (P3.675io.33)4.olO16. Refinement of the cell parameters based on new XRD data shows that a = 6.7515 +o,ooo5/~, b = 6.9625 +0.0005, c = 6.468 _ 0.ooo5, fl = IO3 ~ 53', giv-ing a cell volume of 295.2/~3. Space group P21/n. CONTINUED work by the authors on other rare earth phosphates has led to a re-examination f the type material (MI 2888I) * of the mineral cheralite as described by Bowie and Horne (I953) from Kuttakuzhi, Travancore (now in Kerala State), India. Instrumental improvements during the last quarter century permit us to give new and better quality data for cheralite to improve the specification of the type material whilst in no way detracting from the value of the original descrip-tion. Cheralite (REE,Th,Ca, U)(P, Si)04, is part of an isostructural series of monoclinic minerals of the general form AB04 where A = REE, Th, U, Ca and B = P, Si, Monazite (REEPO4--Breithaupt, I829) and huttonite (ThSiO4--Pabst, I95o) are pro-minent end-members of this series. Microprobe analysis. The original analysis of cheralite (Bowie and Horne, 1953) and subsequent analyses (Finney and Nagaraja Rao, I967; Aplonov and Petrova, 1965) have not separated the individual rare earth elements beyond giving results for CezO 3 and La20 3 or (La, Pr, Nd,Y)203. The present analysis using a Cambridge Scientific Instruments Microscan 5 electron microprobe has permitted all the rare earth elements to be identi-fied. This analysis for 26 dements i given in Table I and has been obtained using the techniques and * Numbers preceded by M I refer to specimens in th