SoMP: IVYAKlTK-UEARlXCi R()('KS ERO.U TALE FjASTEliX nOEDFTELDS, 
Westerx Australia. IT 
tho '‘knots” l)oini>- inon^ or h'ss (‘(iiudinunisional hul olhorwisc witlumt ionn. 
Indeod so weak has boon tho for(M* ot‘ orystallisati<tn of tho ainlalusito lliat 
crystals have in most cases entirely failed to ('lt*ar tliomsoi\(‘s of inclusions, 
wliich consist of tioAvino- ai'ii'rL'^’ates of (|uarl/ ;i**ranulos, finely dixidod dusty 
.li'iaphitic inatfu-ial, shreds of mica, and scatter(Hl ytdlow rutile iuuhUos, identi- 
cal and continuous with tiio inateiial of tlie matrix which surrounds llu'se 
I)oi'])hyro))lasts. Only seldom has the anda]usil(‘ d('velo|KMl (dear cixstals 
sliowino* any seuiblaiu'e of form, but where setm llu‘se usually show charact(‘r- 
istic ]n’isinatic (110) (deavaye and have uuah'rattdy low' r('li(‘f, w(‘ak i)ii-(‘- 
fringeuce, straight extinction iit (douf'‘aled st'cfioiis, lu'^'ativc' eion^ation and 
ne^’ative optical character. A few sections occasionally show a faint ph'o- 
chroism from Z — i)ale pink, to X and Y — coloindess. 
Kyanit(' is present as pori)hyrohIasts in a few s]>e('iniens (e.g. 5084, 
5082, 017205) ami usually 1‘orms rather irregular shap(‘d (‘longat(*d crystJils 
or occurs in g-ranular ag‘g'r(‘g'ates indifaiting an early stage of gi'OAvth. The 
kyanite is soiuetinies partially encIos(*d in granular aggn’t^gates of andalusiti' 
from which it is (Uw eloping, or it may occur as isolatcal porphyrohlasts in the 
(juarlzite matrix. (See Fig. 5A.) It is (*asil\ di'^l iuguisluMi from llu‘ andalusite 
by its high relief and conse(]nent darken' a{>pearance, and by its typii-al 
l)laded form, cleavage, extinction angle, stronger birefringence and posit i\'e 
elongation. Twinning on (100) Axas noticed in se'veral crystals. Though 
characteristically shoAving a. much stronger force of crystallisalion than li’^‘ 
andalusite, crystals are neven’ entirely fre(? of inclusions of (luartz granuh^s, 
curl)onaeeous material and some rutile m^edles, AvhiU' tlu‘ terminations of tin' 
crystal blades are usually i)roken into granula)' aggregates and 0 (-casionally 
1 ‘esolved into needle-crystals of sillimanite. 
Silliiuanite is present in se\'(U'al specinums (I’dlOo, 10833) usually ass<tei- 
ated Avith and de\eio])ing dire('tly fT’om gi'anular andalusite (Se(‘ Fig. 5P>). 
It occurs ill slender elongated and cross-fraclunMl prismatic crystals or in 
felted masses of acicular fibres, gimeraily lying in parallel opti('al orientation 
with th(‘ andalnsittL Th(*se are distinguisht'd from ihi' andalusite by their 
form, higher relief, stronger birefringence and jmsitive elongation, and wher(3 
associated wutli granular kyanite, from this mineral by their s1i*aighl (‘xtinc- 
tion. 
The matrix enclosing the [lorphyroblasts (-(insists mainly of a line 
granular lepidoblastic aggregate of quartz, charged Avith some finely dix ided 
carbonaceous material, t(^gother with s(*attered oriented shiu'ds and Oakes of 
s(*i‘icite, and fr(>quently abundant tiny vidlow grannl<'s and i>risms of rutile. 
Accessory minerals im-liule small (|uaii1ities of iron-ore — liotli lieniatite 
and Jimonite, and also occasional limonite t)seudonu)i'phs aft(*r pyrite. frag- 
ments of brown mica, and a fexv zicrons, all distributed sporadically through- 
out both the matrix and the jiorphyroblasts. 
Thus the Mt. Leonora rock may he .said to vary in mineralogi('al c(mi- 
Itosition from andalusite-()uartz s(-hist or (puirtzite, to kyanite, and sillimatiile- 
bearing aridahisite-quartz schist. Their similarity of chemical com])osition is 
clearly denumstrated, hoAA'ovcr, in the analyses quott'd beloxv. (A) and (!>). 
Their essentia] similarity to the Camel Humps ro('k is also xery n()ti(-(*al)l(', 
tho chief mineralogical dilferences arising from diffei-ences in tenqx'raturt' 
and pressure conditions during nietainorphism, as will b<‘ discussful in a 
later s^^ction. 
