AGATE

Agate is an oxide of silicon and therefore a member of the silicate group. It is a form of quartz but differs from chalcedony in that it has different coloured bands due to the presence of impurities. These make it's colour variable. It is also softer (6.5 on the mohs scale).

It can have different forms such as moss agate and onyx. Samples can be enhanced by dying because it is porous. It can be used for jewellery and ornaments and also in industry as a polisher.

It forms in small round nodules of lava e.g. basalt and in layers and can be found in Brazil, Uruguay, China, Egypt and Scotland.

HOWLITE

Howlite is a silicate which often resembles turquoise. Sometimes tests may need to be carried out to fully identify samples. The main difference is that howlite is much softer. Howlite is 3.5 on the mohs scale whereas turquoise measures 5-6. Consistent colour throughout the sample may also indicate that a sample is more likely to be stained howlite than turquoise.

It is white when pure and is often stained to look like turquoise. It is named after Henry How of Canada who first described it.

It is very heat resistant and has no cleavage.

It often occurs with borax and colemanite. It can be found in Nova Scotia (Canada) and California (USA).