Gem is a rather indeterminate description for a wide range of
precious or semiprecious stones and minerals that are cut and
polished for use in jewelry or as ornaments and trinkets. I this
chapter the term is used, somewhat arbitrarily, to designate
various minerals and stone types that are cut and polished primarily to bring out the beauty and imagery of the stone as
such; these are not all gems that are worked into jewelry. They
include jasper, a rock type much akin to agate, as well as malachite and opal. Of particular interest in this series is 'Pietra
Paesina' from Tuscany in Italy, of which several remarkable
examples are presented in this chapter. For an explanation see
'Pietra Paesina' hereunder.
P
SOUR The artistry in this polished slab of
Paesina Stone could be mistaken for a detail of a marine painting from the 17th century Dutch school. Actual size 130 x 160
mm.
The nature of Paesina Stone is explained in detail under Pietra
Paesina, see below.
TERRA 0
OThis sweeping landscape is laid out
in a little slab of Paesina stone from Tuscany. Actual size 80 x
100mm.
GEM
ed sediment of finely alternating, calcareous silts and clays.
Subsequent deformation and diagenetic processes introduced
little cracks and displacements in the rock as well as dendritic
precipitation of manganese. Even electro-chemical processes
have been proposed in an attempt to explain the complex
structures in this amazing rock. Certainly, the forces that acted
must have been as subtle and original as the refined artistry
found in this stone. Other plates in this chapter show some
more examples of Paesina Stone. Actual width 120 mm.
SO GL
Songlines are the spiritual routes of travel and
dance across Australia as traversed and worshipped by the aboriginal people of that continent. In this fist-sized, polished chunk
of jasper from Roy Hill in Western Australia (see next plate)
one might see a microcosmic version of the songlines.
OY HILL
C
S This type of jasper is found in
the vicinity of Roy Hill, a remote post in the outback of
Western Australia. In the course of geologic time this type of
rock has been partially stained red by iron.
The remaining, unstained patches often take on enigmatic
shapes, like the 'dramatis personae' in the polished slabs here
juxtaposed. Actual size 100 x 120 mm.
ble', is an amazing type of stone found in the Tuscan hills around
Florence. The ancients already considered it a material worthy
of a craftsman. By origin this rock was a lake- or river-depositPAESI
PUI Tepuis are the notorious, flat-topped
mountains located in the savanna region of southern Venezuela.
The slopes of these high and isolated mountains are so steep
and inaccessible that each has a particular fauna and flora, often
including unique species found nowhere else. The tepui here
depicted is an allegory, seen in a small, polished slab of Paesina
stone from the rolling hills ofTuscany. Actual size 90 x 120 mm.
DF
0 Pebbles of this type of rock, which is akin
to Paesina Stone, are found in the valley of the Arno River in
Tuscany, Italy. Although probably formed by similar processes
to those that created the patterns in Pietra Paesina (see
below), the structures in Verde d'Arno are more geometric.
These could have inspired painters like Lionel Feininger or Paul
Klee. Actual size of this polished face is 70 x 90 mm.
PIET
s Pietra Paesina, also known as 'ruin-mar96
SPEC OL F Spectrolite, also called labradorite, is a variety of the extensive group of rock-forming minerals called
feldspars. large, tabular crystals often display iridescence, a
changeable and magic emanation of colors resulting from the
interference of light reflected by the semi-translucent, lamellar
crystal planes. Actual size 40 x 50 mm.
o
E Cordierite is a characteristic mineral formed
by alteration in highly metamorphic rocks. It is akin to beryl,
and clear crystals of appropriate color are sometimes used in
jewelry. The crystals are often transected by fissures, along
which replacement by other minerals takes place. That feature
is called 'pinitization' and it is well displayed in this thin section.
OPAL Opal is hydrated, amorphous silica, deposited from silica-bearing waters in voids and fissures of certain rock formations. Water molecules trapped in the silica account for the
milky luster and brilliant pastel colors that make opal into such
a desirable precious stone. Much of the high-quality opal traded
these days comes from Australia. A number of years ago this
precious or semiprecious stones and minerals that are cut and
polished for use in jewelry or as ornaments and trinkets. I this
chapter the term is used, somewhat arbitrarily, to designate
various minerals and stone types that are cut and polished primarily to bring out the beauty and imagery of the stone as
such; these are not all gems that are worked into jewelry. They
include jasper, a rock type much akin to agate, as well as malachite and opal. Of particular interest in this series is 'Pietra
Paesina' from Tuscany in Italy, of which several remarkable
examples are presented in this chapter. For an explanation see
'Pietra Paesina' hereunder.
P
SOUR The artistry in this polished slab of
Paesina Stone could be mistaken for a detail of a marine painting from the 17th century Dutch school. Actual size 130 x 160
mm.
The nature of Paesina Stone is explained in detail under Pietra
Paesina, see below.
TERRA 0
OThis sweeping landscape is laid out
in a little slab of Paesina stone from Tuscany. Actual size 80 x
100mm.
GEM
ed sediment of finely alternating, calcareous silts and clays.
Subsequent deformation and diagenetic processes introduced
little cracks and displacements in the rock as well as dendritic
precipitation of manganese. Even electro-chemical processes
have been proposed in an attempt to explain the complex
structures in this amazing rock. Certainly, the forces that acted
must have been as subtle and original as the refined artistry
found in this stone. Other plates in this chapter show some
more examples of Paesina Stone. Actual width 120 mm.
SO GL
Songlines are the spiritual routes of travel and
dance across Australia as traversed and worshipped by the aboriginal people of that continent. In this fist-sized, polished chunk
of jasper from Roy Hill in Western Australia (see next plate)
one might see a microcosmic version of the songlines.
OY HILL
C
S This type of jasper is found in
the vicinity of Roy Hill, a remote post in the outback of
Western Australia. In the course of geologic time this type of
rock has been partially stained red by iron.
The remaining, unstained patches often take on enigmatic
shapes, like the 'dramatis personae' in the polished slabs here
juxtaposed. Actual size 100 x 120 mm.
ble', is an amazing type of stone found in the Tuscan hills around
Florence. The ancients already considered it a material worthy
of a craftsman. By origin this rock was a lake- or river-depositPAESI
PUI Tepuis are the notorious, flat-topped
mountains located in the savanna region of southern Venezuela.
The slopes of these high and isolated mountains are so steep
and inaccessible that each has a particular fauna and flora, often
including unique species found nowhere else. The tepui here
depicted is an allegory, seen in a small, polished slab of Paesina
stone from the rolling hills ofTuscany. Actual size 90 x 120 mm.
DF
0 Pebbles of this type of rock, which is akin
to Paesina Stone, are found in the valley of the Arno River in
Tuscany, Italy. Although probably formed by similar processes
to those that created the patterns in Pietra Paesina (see
below), the structures in Verde d'Arno are more geometric.
These could have inspired painters like Lionel Feininger or Paul
Klee. Actual size of this polished face is 70 x 90 mm.
PIET
s Pietra Paesina, also known as 'ruin-mar96
SPEC OL F Spectrolite, also called labradorite, is a variety of the extensive group of rock-forming minerals called
feldspars. large, tabular crystals often display iridescence, a
changeable and magic emanation of colors resulting from the
interference of light reflected by the semi-translucent, lamellar
crystal planes. Actual size 40 x 50 mm.
o
E Cordierite is a characteristic mineral formed
by alteration in highly metamorphic rocks. It is akin to beryl,
and clear crystals of appropriate color are sometimes used in
jewelry. The crystals are often transected by fissures, along
which replacement by other minerals takes place. That feature
is called 'pinitization' and it is well displayed in this thin section.
OPAL Opal is hydrated, amorphous silica, deposited from silica-bearing waters in voids and fissures of certain rock formations. Water molecules trapped in the silica account for the
milky luster and brilliant pastel colors that make opal into such
a desirable precious stone. Much of the high-quality opal traded
these days comes from Australia. A number of years ago this