Garrawilla Volcano
About 200 million years ago all hell broke loose in this area. Massive pyroclastic explosions and lava flows, above and below ground, from numerous vents, created a huge pile of volcanic debris, about 130 km in diameter.
The Garrawilla volcanics are located on the southern rim of the Great Artesian Basin and is thought to be on the shoreline of an ancient lake called Lake Walloon. Lake Walloon may have once covered an area of well over 1 million square Km.
Due to the tension on tectonic plates during the breakup of Gondwana deep crustal fractures formed. These provided a pathway for lavas and intrusions to reach the surface. The period of intermittent volcanism lasted from the middle Triassic period well into the Cretaceous period. Their height may have exceeded their current height by more than 500 to 1000m. This was due to a build-up of volcanic debris from explosive / pyroclastic eruptions. At its peak the Garrawilla volcano would have appeared as a mountain range closely resembling the present-day Warrumbungle ranges. Lava and ash flows reached as far as Dubbo, Narrabri, and Coonamble.
During its long volcanic period this volcano has been repeatedly eroded and covered by the sea/water serval times.
The first eruption of the Garrawilla volcano came up through wet cool swamps which produced large cavities called vugs. One lava flow, partly exposed today, produced most of the zeolite crystals on display here. We estimate this lava flow to be about 40 km long and about 7 km wide. The crystals formed in cavities in the basalt, with some of them big enough to stand up in. By the size of some of our crystals, it is believed that it took the lava up to a 1000 years to cool down. The cavities here are larger than anywhere else in Australia for zeolites and some crystals found are larger than anywhere else so far discovered in the world. The cavities found were up to 3m long. The average size of a zeolite cavity is 3 millimeters. With 3cm being considered large. The Garrawilla volcano produced the spectacular zeolites and associated crystals such as stellerite, heulandite and prehnite. These are on display in the museum at Crystal Kingdom.
Zeolite crystals usually tiny to microscopic with no colour. Some of these on display in our museum are much larger and have more vivid colour than those found anywhere else on earth.
Zeolite means boiling stone, they have a lot of water in them and when heated will give off their water with a spurt and then will take into their structure elements such as aluminum, ammonium and other heavy metals.
As different crystals form at different temperatures. This is why you can have up to four or five different crystals in one vug/ cavity. Calcite crystals filled the last space in these vugs due to a period of being under salt water. Calcite can be dissolved in an acid bath to expose other crystals. This has been done with our specimens in the museum.
In the Late Jurassic/Early Cretaceous Period, when a large part of the continent was under water, the Garrawilla Volcano jutted out of this sea as an island or peninsular.
Gallery
Garrawilla
Remnants of the central part of the Garrawilla Volcano.
Garrawilla
Remnants of the central part of the Garrawilla Volcano.
Stellerite
Stellerite: Ca (Al2Si7O18) 7 H2O
Crystal System: Orthorhombic
Stellerite is the predominant zeolite crystal in this area. There are only two places in the world where large crystal are found and the best ones come from the Garrawilla volcanics.
These crystals are found in cavities or seams and range in size from a few millimeters to large crystals up to 180 mm long, indicating a very slow cooling of the lava.
Stellerite
Stellerite: Ca (Al2Si7O18) 7 H2O
Crystal System: Orthorhombic
Stellerite is the predominant zeolite crystal in this area. There are only two places in the world where large crystal are found and the best ones come from the Garrawilla volcanics.
These crystals are found in cavities or seams and range in size from a few millimeters to large crystals up to 180 mm long, indicating a very slow cooling of the lava.
Heulandite
Heulandite: (Ca,Na)2-3Al3(Al,,Si)13O36– 12 H2O
Crystal System: Monoclinic
Heulandite is normally found as small, 3mm, crystals. There are only a few localities in the world that produce large crystals.
Our specimen are regarded as the largest and most colourful heulandite crystals in the world.
These crystals are found in cavities in the host rock and range in size from 1mm to 80mm and are colourless, pink, orange and brown.
Heulendite
Heulandite: (Ca,Na)2-3Al3(Al,,Si)13O36– 12 H2O
Crystal System: Monoclinic
Heulandite is normally found as small, 3mm, crystals. There are only a few localities in the world that produce large crystals.
Our specimen are regarded as the largest and most colourful heulandite crystals in the world.
These crystals are found in cavities in the host rock and range in size from 1mm to 80mm and are colourless, pink, orange and brown.
Prehnite
PREHNITE: Ca2 Al (OH2) Al2 Si3 O10 (OH)
Crystal System: Orthorhombic
Prehnite is found in a number of localities in Australia, mostly as solid masses in cavities in basalt.
The “finger-like” crystals on display here are very rare and normally no longer than 2 cm long. Because of their shape and the location they are found in, we believe that they grew in a mineral-rich hot spring or developed in very large cavities.
This is the only location in the world where the crystals are more than 2 cm long and the golden colours are found.
Only a very small deposit is known in the Garrawilla volcanics.
Prehnite
PREHNITE: Ca2 Al (OH2) Al2 Si3 O10 (OH)
Crystal System: Orthorhombic
Prehnite is found in a number of localities in Australia, mostly as solid masses in cavities in basalt.
The “finger-like” crystals on display here are very rare and normally no longer than 2 cm long. Because of their shape and the location they are found in, we believe that they grew in a mineral-rich hot spring or developed in very large cavities.
This is the only location in the world where the crystals are more than 2 cm long and the golden colours are found.
Only a very small deposit is known in the Garrawilla volcanics.
Stellerite and Laumonite
Laumontite: Ca (Al2Si4O12) 4 H2O.
Crystal System: Monoclinic.
These crystals are found in association with heulandite and stellerite.
Stellerite and Black Druzy
Drusy Quartz: SiO2.
This occurs as plates of different colours, from clear through white, pink, yellow, green and black, or in association with some of our other minerals, in some instances completely covering the stellerite crystals.
Dogstooth Calcite
Calcite: Ca CO3
Crystal System: Hexagonal
Calcite occurs in many different forms and shapes.
Pointed crystals are called “Dog Tooth” crystals, if it splits on a flat plane it is called “Iceland Spar” and if this is transparent, it is called “Optical Calcite”.
Iceland Spar always retains it’s rhomboid shape when it is broken up.
Calcite is the last mineral to crystallize in some of the cavities and sometimes completely fills them.
Calcite often covers other crystals; to recover them, calcite can be dissolved in hydrochloric acid.
Natrolite in Calcite
Natrolite: NA2 (Al2Si3O10) 2 H2O,
Crystal System: Orthorhombic.
This is found mostly in the younger basalts.
Stellerite and Heulendite on Quartz
A personal favourite of mine.
Garrawilla Cross section
Diagram showing earth strata layers.