Crop productivity in Tanzania is generally low and this is partly due to inadequate and poor retention of plant nutrients and moisture by some soils. The country has several vermiculite deposits, but none of them are exploited to improve the soil properties because of lack of information on their potential suitability. The aim of this research was to establish the suitability of vermiculites from Tanzania as soil improvers for crop production through characterization. The study involved five samples from Tanzania and one from South Africa, which was included for comparison purposes. Mineralogy of the samples was studied by a combination of X-ray diffraction (XRD) and scanning electron microscopy (SEM) fitted with energy dispersive system (EDS), whereas electron probe microanalysis (EPMA) and inductively coupled plasma-mass spectrometry (ICP-MS) were used to establish elemental compositions. Extractability of some heavy metals in vermiculites was assessed by diethylene triamine pentaacetic acid extraction (DTPA), whilst extractable P was determined by acetic acid extraction. The pH, water release characteristic, and cation exchange capacity (CEC) were among the physical and chemical properties assessed. Pot and field studies were then carried out in Tanzania to assess maize response and retention of macronutrients in a sandy soil amended with vermiculites. Maize was used as a test crop. The results found indicate that not all samples are vermiculites, some are hydrobiotites. Analysis shows that none of them contain hazardous accessory minerals. However, some have elevated concentrations of Cr and Ni, but these heavy metals are insignificantly plant available and do not inhibit the uptake of essential plant nutrients. Hence, the studied vermiculites are safe to exploit for crop production. In addition, all are slightly alkaline with high CEC and, thus, they are suitable as a growing medium with ability to retain plant nutrients from leaching. However, heating above 600 °C should be avoided as it reduces the CEC of vermiculites by more than 90 % and makes some of the exfoliated products strongly alkaline and, thus, unfavourable for crop production. The Tanzanian vermiculites can retain plant-available water but their ability is less than vermiculite from South Africa. The P in these vermiculites is extractable and extractability increases on heating to 400 °C. Further heating makes P insoluble and less extractable. Maize vegetative growth, dry matter yield, and nutrient uptake were significantly enhanced by adding vermiculite to the soil over the control. In addition, it retained and fertilized the soil with P. Pre-heated vermiculite at 600 °C performed better than unheated vermiculite and it inhibited the fixation of the applied K and N. It was concluded that the Tanzanian vermiculites have a recommendable potential of improving soil properties for crop production when heated at a temperature of not more than 600 °C. However, more field trials are recommended on other types of soils and crops other than sand and maize used in order to widen the scope of their utilization in Tanzania.Commonwealth Commission in the United Kingdom