Moonstone Hill, Blackbraes National Park, Flinders Shire, Queensland, Australiai

Regional Level Types
Moonstone Hill	Hill
Blackbraes National Park	National Park
Flinders Shire	Shire
Queensland	State
Australia	Country

A low isolated hill on the east side of the Kennedy Developmental Road (unsealed) about 90 km south of The Lynd.

The locality is within the Chudleigh Late Cenozoic basaltic Province, which is characterised by broad, partly-dissected lava plains between numerous pyroclastic cones, some composite cones and several lava shield volcanoes. Moonstone Hill is one of several scoria vents that are surrounded by flat-lying basalt lavas, some of which were erupted from the vents. Scoria (lava with a high proportion of gas bubbles) is exposed on top of the hill and is typically reddish-brown in colour, and characterised by its vesicular texture. The feldspar fragments occur as megacrysts filling some gas cavities in the lava, and has been identified as anorthoclase, which is unusual as anorthoclase-moonstones are uncommon and somewhat of a rarity for collectors.

Generally the material is colourless and transparent, but some is milky white to yellowish and translucent to opaque. Some specimens show a silvery-white to bluish adularescence (presumably because of separation into albite and orthoclase crypto-perthitic layers) and hence can be classed as moonstone.

Gem-quality material commonly occurs as blocky cleavage fragments of 10–30 carats and rare specimens 5–6cm in length. A lot of material is unusable for cutting due to incipient cleavages, or fractures and other inclusions, but clean sizeable material is common. The material has weathered out of the host rock and can be found on the ground surface or in the soil around the lower flanks of the vent.

Specking the ground surface and simple shallow excavation and dry sieving are the best methods to use.

Other Regions, Features and Areas containing this locality

References