$B!!%9%Z%$%s!"%T%l%M!<;3L.$N%U%i%s%99q6-$K6a$$;3Cf$N%"%k%,@nN.0h$K=cEY$N9b$$C:;@%^%0%M%7%&%`$+$i@.$kI)6lEZ9[$N:=$,H/8+$5$l$?$N$O(B1945$BG/$N$3$H$G$7$?!#(B
$B$=$N8e$NDI@WD4::$K$h$j2$,H/8+$5$l$^$7$?!#(B
$BMO9[O'$NBQ2PN{4$:`$H$7$F:N7!$5$l$kI)6lEZ9[$NKdB"NL$O(B30$B!A(B60$BG/J,$H?dDj$5$l!"8=:_$bG/4V(B50$BK|%H%s$,:N7!$5$l$F$$$^$9!#(B
$B!!$3$N9[;3$,0lLv@$3&$K9l$$$?$N$O!"$7$+$7I)6lEZ9[$G$O$J$/:GBg$G$O(B20cm$B$K$bC#$9$k8+;v$J6l3%@P$N7k>=$,==F6$NH/8+$G$7$?!#(B
$B!!>=F6$OF~$j8}$N9-$5$,(B50$B-V!"?<$5$,(B20m$B$NBg$-$5$G!"9[;3$N3+H/$r;X4x$7$?
$B!!>=F6Fb$rKd$a?T$/$7$?7k>=$O$=$N2ACM$rD>$A$KG'<1$7$?%3%k%I%P$K$h$C$FCz=E$K:N7!$5$l!"I8K\$H$7$F(B1965$BG/0J9_!"@$3&$NGnJ*4[$d%3%l%/%?!<$KHNGd$5$l$^$7$?!#(B
1970$BG/$N%3%k%I%P$N;`8e7k>=$N6!5k$O5^8:$7!"(B1980$BG/0J9_?7$?$KH/8+$5$l$?7k>=$OI=LL$,7c$7$/M;?*$5$l$F$$$?$jE4$d%^%s%,%s;@2=J*$N;,$GJ$$o$l$F$$$?$j$H!"0JA0$N7k>=$HHf$Y$k$HCx$7$/IJ=F6H/8+$N2DG=@-$O;D$C$F$$$^$9!#(B
$B!!@>%T%l%M!<;3L.$N8E@84d(B(2.25-5.7$B2/G/@N(B)$BCf$KO*=P$9$k$3$N9[>2$N@.0x$OL@$i$+$G$O$"$j$^$;$s!#$,!">xH/4d$G$"$C$?6l3%@P$NBO@QAX$K%^%0%M%7%&%`J,$KIY$`(B350$B!n0J2<$NDc29$NG.?e$,4SF~$7$F8rBe:nMQ$,5/$3$j!">=F6Cf$K5pBg$J6l3%@P$N7k>=$,@.D9$7$?$H$$$&$N$,:G?7$N@b$G$9!#(B
$B$3$l$O%V%i%8%k!&%P%$%"=#!"%V%k%^!<%I$N%^%0%M%5%$%H9[;3$NNc$H$[$\F1$8@.0x$H9M$($i$l$^$9!#(B |
$B!!(BMagnificent dolomite crystals from quarries near Eugui, Navarra, Spain,
first reached the mineral market around 1965, and were inmediately hailed
as new "classics." It was in 1945 that an unusual discovery was
made along the Arga River near Eugui, Navarra, Spain . It was found that
the river sand was composed mainly of the mineral magnesite, MgCO3. Following the detailed survey and beds of magnesite were discovered along
the southwest bank of the river. Quarrying operations under the direction
of Chief Engineer Juan Cordoba encountered large, crystal-filled pockets
measuring up to 50 meters square and 20 meters deep. Fortunately, Cordoba
recognized the great mineralogical value of the beatutifully crystallized
domomite, and took steps to preserve a large number of specimens. These
he sold to major museums throughout the world and also to private collectors,
beginning around 1965. Following Cordoba's death in 1970, the supply of
specimens quickly diminished. The quality of recent material is inferior
to that of the old specimens preserved by Cordoba; the crystal faces tend
to be frosted, are sometimes more deeply corroded, and are usually stained
by iron and manganese oxide. However the quarries are still active to produce
with annual production of 500,000 tons of magnesite ore, mainly for furnace
brick production. Consequently it is still possible that new pockets will
be encountered.
$B!!(BThe magnesite-dolomite deposit crops out in the Paleozoic rocks of the
Western Pyrenees. The origin of the carbonate units reaching a thickness
of 180 meters is still unclear. One hypothesis suggests direct precipitaion
of magnesite in a lagunal environment. And a more recent theories suggest
a metsomatic origin in which original dolomitic sediments are replaced
by magnesite through the action of Mg-rich hydrothermal fluids . A period
of partial re-dolomitization is said to have followed, resulting in the
formation of large pocket of dolomitic crystals.
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