Malachite
FOSSICKING IN SOUTH WEST VICTORIA
South west Victoria is predominately a farming area. Warrnambool, the regional centre, is located on the
coast and has a population of some 30,000 people.
Fossicking sites are limited in the region as most land is privately owned and generally inaccessible to
fossickers. Currently (2016) club members fossick at the quarry at Mt Shadwell in Mortlake. Two other
localities near Warrnambool which we previously accessed are also described below.
These locations are:
1. The Mount Shadwell quarry (operated by the Moyne shire) which is
located at Mortlake, some 45km inland (north) of Warrnambool. The quarry produces road making
materials (different grades of scoria). In the quarry volcanic "bombs" can be found, some of which contain
gem peridot.
If you are visiting Mt Shadwell for fossicking, be aware that it is only possible
to fossick on Friday, Saturday and Sundays.Bookings are essential, to book
please contact the Moyne Shire Information centre (03) 5599 2899 between
10am and 4pm Monday to Thursday or 0456 700 862 between 10am and 4pm
Friday to Sunday.Visitors are required to follow an induction session and sign
an indemnity form.!
Over recent years club members have been finding increasing amounts of orange/golden/yellow peridot
as well as the "normal" green peridot. Many variations in between these two extreme colours have also
been found. Typically the rich green peridot has been found in the black scoria in the quarry whereas the
"golden peridot" has been located in the red scoria. However this is not always the case, as single bombs
can be found containing both yellow and green peridot as well as many other colours in between these
two extremes.
Peridot is the name generally given by lapidary enthusiasts to gem quality olivine. Olivine is a
"magnesium iron silicate" which follows the
formulae (Mg,Fe)2SiO4. This mineral is one of an
isomorphous series which varies from the
magnesium silicate "forsterite" (Mg2SiO4) to the
iron silicate "faylite" (Fe2SiO4). this variation in the
amounts of iron and magnesium influences the
different colours in the peridot found at Mortlake.
Several of our club members have good
collections of faceted peridot which show the
variation in colours present in the material that can
be fossicked from Mt Shadwell. The photos show
some faceted gems cut by Brian Alexander and
Alan Wood, (Warrnambool Gem Club members), a ‘volcanic bomb’ and a view of the quarry. The gems
range up to 4.6ct in weight and provide a good indication of the wide range of colours available. The
larger gems often contain small inclusions but still cut very attractive gemstones.
Fossicking for Peridot at Mt Shadwell
Mt Shadwell is well known locally for its volcanic bombs, which range in size from a few centimetres across to huge
specimens over a metre long; although the majority of bombs would measure around 10 to 15cm in diameter. Most of the
bombs have spectacular olivine cores with a thin coating of scoria on the outside. Unfortunately, the olivine core usually
consists of small crystals the size of grains of sugar. The bombs which we gem hunters seek are those which contain
peridot of a size suitable for faceting. You generally have to break open many of the "sugary bombs" before you strike a
"gemmy" bomb with suitable material within it. If you are lucky you may also find an occasional bomb yielding anorthoclase
of a size suitable for faceting a nice gem.
Mt Shadwell is the type of place you can visit and find "plenty" or "nothing" if you are looking for facetable peridot. I have
visited the quarry on several occasions when I found no facetable material, while at the same time some of my
companions were finding nice bombs with gem material within. However, my last 7 visits have yielded several bombs
containing good gem material each time. Each "good bomb" can yield several "cutters". So like many fossicking locations,
you have to be digging in the "right spot" at the "right time"!
During the last 12 months our club has hosted visits by several clubs, both Victorian and interstate.
If you plan to visit Mt Shadwell quarry, you should first visit the Moyne Shire offices at 1 Jamieson Ave., in Mortlake to
sign a consent form. The staff at the shire offices are very helpful and can put you in contact with Alan Wood, a
Warrnambool Gem club member who lives in Mortlake (except when he migrates north during winter, on fossicking trips)
and who is usually only to happy to help visiting fossickers.
Alan has become the local "expert" on the minerals to be found at Mt Shadwell. He has an excellent collection of
"gemmy bombs" from the Mount and a good display of peridot gems which he has faceted from such bombs. While locals
take these "bombs" for granted, there are very few places in the world where such volcanic bombs can be found. Calcite
"micromount" specimens can also be collected at Mt Shadwell with little difficulty.
While you are at the quarry, a good place to look for the peridot is in the large stockpile of "volcanic bombs" that the
quarry operators (the Moyne shire) stockpile for fossickers to work through. Many good pieces of peridot have been
obtained from that stockpile!
When visiting the quarry you should wear a high visibility vest and follow the directions of the quarry foreman. The main
equipment you need is a good geo pick/hammer and something to carry your finds in. Good footwear and long trousers
are also essential.
Notes:
1. Isomorphism: is the phenomenon where the atoms of one element (such as Fe, iron) replace the atoms of another
element (such as Mg, magnesium) in the crystal lattice to produce a continuum of minerals between the two extremes.
Some cut gems by
A.Wood, Mortlake
olivine. 2018
One of the better
volcanic bombs
Alan has found!
Many gems were
cut from the other half
of this bomb.
Two faceted gems from
Mt Shadwell, L.H. gem
18 mm long.
2. Lake Keilambete (‘Fentons quarry’, privately owned) which produces limestone for soil
conditioning purposes and for road material. A variety of fossils including sharks teeth can be found at this quarry.
PLEASE NOTE THAT THE CLUB HAS BEEN UNABLE TO CONTACT THE QUARRY OWNERS SINCE 2013 AND SO HAVE NOT
BEEN ABLE TO ACCESS THE QUARRY.
Lake Keilambete near Terang is a half hour drive east of Warrnambool. Here fossickers can search for marine fossils in
Ian Fenton’s limestone quarry on the edge of the lake. Lake Keilambete is a maar volcano, approximately 50,000 years old,
located some 4km northwest of Terang. There are many such maar volcanos in the western district. They result from
explosions occurring when hot magma rises into rocks which are not far from the surface and which contain lots of ground
water. High pressure steam is produced, which blasts the magma and surrounding rocks into clouds of small fragments.
Lake Keilambete’s circular crater, which resulted from such an
eruption/explosion, is quite beautiful. It is some 2.4km in diameter and
40m deep, with the lake up to 9m deep. (Ref. 1) The crater is
surrounded by a tuff ring with limestone below the tuff. It is this
limestone and tuff that is mined in the quarry and it is in the limestone
that the fossils can be found.
Ian Fenton had been operating the quarry since the late 1960’s for
material to make farm tracks with the limestone also being used for ‘soil conditioning’. Over that time Ian collected a good
set of fossils. Of particular note is his very impressive collection of fossil sharks teeth, one of which is shown below. Ian has
since sold the quarry.
During field trips a number of impressive fossils have been collected. At the quarry a variety of 40 - 50 million year old
fossils can be found, ranging from whale vertebrate and the sharks teeth to many different types of shells. Fossickers
wishing to visit the quarry would need to contact/locate the ‘current’ owners prior to visiting the area. The photos show the
quarry next to the lake plus a fossil shark’s tooth.
‘Tarrone’ quarry is located a half hours drive north-west of Warrnambool. This quarry, which is not
open to the general public, is a working quarry and is inaccessible during the week when excavation and blasting work is
undertaken. It is necessary to obtain special permission if you wish to fossick there, and members of the Warrnambool
were only able to obtain access the quarry because a club member worked at the site. The club has not accessed the site
for several years. The field trips to Tarrone enable the collection of zeolite specimens; club members having found a
number of beautiful aragonite and calcite specimens in recent visits. The fossicking involves the use of hammers and rock
chisels in the breaking open of basalt boulders in the search for minerals/crystals. Typical finds include calcite crystals plus
aragonite and augite specimens, some of which are shown in the photos below.
References:
1. Volcanoes in Victoria, Royal Society of Victoria, W.Birch, 2000