Radioactivity in minerals are caused by the inclusion of naturally-occurring radioactive elements in the mineral’s composition. The degree of radioactivity is dependent on the concentration and isotope present in the mineral. For the most part, minerals that contain potassium (K), uranium (U), and thorium (Th) are radioactive.

Radioactivity is an attribute of minerals that contain radioactive elements. Radioactive elements are elements that contain disintegrating nuclei, emitting alpha rays, beta rays, and gamma rays. Uranium and thorium are the best known radioactive elements. Minerals that contain these elements in their chemical structure will be radioactive.

Radioactive minerals are unstable, meaning the elements in their structure continually break down. This destroys the mineral’s crystal lattice, causing it lose its crystal shape. When this happens, its crystal edges become rounded, and the mineral eventually becomes amorphous.

Radioactive minerals can be identified with special instruments that detect radiation. The device used to measure this is the Geiger counter. Electric charges develop in a Geiger counter when it is placed near radioactive material; this can measure the presence and intensity of radiation. Geiger counters are normally used by scientists and specialists, but collectors may also obtain inexpensive Geiger counters.

Table of Naturally Occurring Radioactive Isotopes

Element	Isotope Symbol	Natural Abundance	Half-life (Years)	Primary Decay Mode
Tellurium	130Te	33.97%	2,400,000,000,000,000,000,000.00
Vanadium	50V	0.25%	390,000,000,000,000,000.00	EC
Zirconium	96Zr	2.80%	360,000,000,000,000,000.00
Samarium	149Sm	13.80%	10,000,000,000,000,000.00	alpha
Samarium	148Sm	11.30%	7,000,000,000,000,000.00	alpha
Osmium	186Os	1.58%	2,000,000,000,000,000.00	alpha
Neodymium	145Nd	8.30%	1,100,000,000,000,000.00	alpha
Platinum	192Pt	0.79%	1,000,000,000,000,000.00	alpha
Indium	115In	95.70%	600,000,000,000,000.00	beta –
Gadolinium	152Gd	0.20%	110,000,000,000,000.00	alpha
Tellurium	123Te	0.89%	13,000,000,000,000.00	EC
Platinum	190Pt	0.01%	690,000,000,000.00	alpha
Samarium	147Sm	15.00%	108,000,000,000.00	alpha
Rubidium	87Rb	27.83%	49,000,000,000.00	beta –
Rhenium	187Re	62.60%	45,000,000,000.00	beta –
Lutetium	176Lu	2.59%	22,000,000,000.00	beta –
Thorium	232Th	100.00%	14,000,000,000.00	alpha
Uranium	238U	99.28%	4,460,000,000.00	alpha
Potassium	40K	0.01%	1,250,000,000.00	beta –
Uranium	235U	0.72%	704,000,000.00	alpha