DUMORTIORITE

A silicate which contains aluminium, boron, oxygen and silica (maybe some iron). It is usually blue but may also be brown, green, pink or violet. It is moderately hard (7 on the mohs scale).

It is highly resistant to heat and is therefore used as a lining for furnaces. This is typical of a mineral that contains aluminium e.g. sapphire. It is nearly always insoluble and is virtually impossible to melt.

It usually occurs in solid lumps and may sometimes be discoloured by iron stains which can be removed by wiping with acid. The best quality samples are polished and made into ornaments or jewellery. Dumortiorite crystals are very rare.

It is named after Dumortier, a French fossil hunter who discovered it.

Dumortiorite forms in aluminium rich metamorphic rocks and in some pegmatite deposits. It is often found interwoven with rock crystal (colourless quartz). These deposits are known as dumortiorite quartz.

It can be found in Canada, France, Italy, Madagascar, Norway, Sri Lanka and California and Colorado (US). Most of the worlds gem quality dumortiorite is from Nevada, US.

EUDIALITE

It is a complex silicate which is most commonly found in nepheline syenite pegmatites. It may be pink, red, brown or yellow in colour depending on variations in it's atomic composition. It is moderately hard (5.5 on mohs scale).

It has a complicated make-up and is very variable and therefore different text books may give a different formula. Eucolite which is a variety of eudialite is softer and calcium rich.

It derives it's name from the Greek words Eus which means good and dialieis which means to dissolve. This refers to it's ability to dissolve well in acids.

Most eudialite is formed in coarse grained acidic and igneous rocks e.g. nepheline syenites and nepheline syenite pegmatites. It is most commonly associated with arfvedsonite, which is a silicate of sodium and iron. It may also be found with aegirine, gibbsite and hydrated silicates of the zeolite group.

It was discovered in Greenland. This is the classic source where it can be found deposited in nepheline syenite pegmatites. It may also be found in Quebec (Canada), Madagascar, Norway, Russia and Sweden.