Many collectors regularly handle minerals without a second thought of anything else but their aesthetic appeal. They then happily pick up a handful of pretzels or nuts, which they consume in blissful ignorance. Yet many of the minerals found in their collections are deadly poisons and they innocently end up ingesting substances likely to cause harm.

Possibly the worst culprit is Arsenic. Many innocuous Arsenate minerals such as Mimetite can give off Arsenic under certain conditions, particularly when wet. So handle these with dry hands. Try heating any Arsenic compound and see what happens. The garlic-like smell so easily given off soon alerts to the presence and danger of Arsenic. Indeed Arsenic is considered so harmful, that special laws were passed in the 19th century to prevent miners contracting Arsenic poisoning through the skin by perspiration or by breathing in the dust from the air. The minerals most commonly found in collections are Realgar and Orpiment - both Arsenic sulphides.

Nearly as poisonous is Antimony. Amazingly for us today, it was at one time much used in cosmetics as a base, and continues to be used on the boxes of safety matches. In fact one of the easiest tests for Stibnite, which is a sulphide of Antimony, is to strike a match on its surface. Other common Antimony minerals include Allemonite, which is a doubly toxic natural alloy of Antimony and Arsenic.

Another of the naturally occurring poisons is Mercury. Silvery drops of this metal are often found in veins of its sulphide, Cinnabar. Indeed Mercury is so easily released from this ore, that only gentle heating is required. Interestingly this makes for a great experiment because the Mercury vapour is a strong absorber of UV. Thus shining a UV light towards a heated cruicible of Cinnabar will produce a black shadow behind the otherwise invisible vapour of Mercury being given off. A word of warning, please don`t try this, and don`t breathe in the fumes!

Two other, closely related, elements should also be treated with care, Tellurium and Selenium. Both are highly poisonous, especially when heated in air, when both oxidise to produce toxic fumes of TeO2 and SeO2. A particulalry nasty mineral we have come across is Coloradoite, HgTe (Mercuric Telluride). This contains a double dose of two harmful substances and should definitely not be handled without some form of skin protection.

Also on the list of very toxic minerals are those containing Thalium. The metal and its minerals are highly poisonous and should be handled with great care. Contact with skin is dangerous because Thallium(I) compounds have a high aqueous solubility and are readily absorbed. Part of the reason for high toxicity is that, when present in aqueous solution as the univalent thallium(I) ion (Tl+), it exhibits some similarities with essential metals, particularly potassium. It can thus enter the body via potassium uptake pathways, but its chemistry is very different and the substitution disrupts many cellular processes.

Other minerals, whilst not being toxic due to their chemical composition, are nevertheless harmful. Examples include minerals belonging to the Inosilicates including Tremolite and Riebeckite. Commercially known as Asbestos, these release long, needle-like fibres that are highly dangerous when inhaled. For similar reasons great care should be taken when cutting or trimming other silicate minerals. Any work should be done in a well-ventilated area, preferably wearing air-filtration masks. Even short-term exosure can lead to the debilitating disease Silicosis.

And finally we come to the radioactive minerals. These are a particular hazard as the effects of exposure are delayed and the materials seem perfectly innocuous at first. Thus it is well worth treating all Uranium and Thorium minerals with great respect.

Overall, there is little reason for any of these minerals to be totally excluded from any collection. But we strongly recommend taking precautions such as washing hands, storage in air tight containers, not breating the dust or fumes given off and definitely keeping out of the reach of children and pets. If not sure, then these minerals are best avoided. Please note that we do not take any responsibility for any advice suggested here and if you collect these specimens you do so entirely at your own risk.