Greensands are regarded as loose, shallow marine sediments that contain a common, yet useful palaeoenvironmental (i.e. past environment) and chemical indicator, a green mineral called glauconite. So far, glauconite has been used as a low sedimentation rate and sea level rise indicator in geoscience. Its occurrence in the United Kingdom indicates, together with other geological evidence, that during the Lower Cretaceous (140Ma-100Ma), the mainland was partially submerged due to higher global temperatures and sea-levels. In this paper, physical and chemical differences between two samples of greensands from New Zealand have been assessed in order to reconstruct a past environment and therefore gain further insight into the formation of this type of sediment. The occurrence of greensands in UK has been theoretically investigated in this study by using data gathered from New Zealand samples. While a new use for glauconite as a past marine acidity indicator has been proposed, further investigations must be undertaken before this can be validated. The overall aim of this paper is to explain a process of thinking and of analysis which starts from sample characteristics and small details that builds up to form a bigger geological picture. This includes novel research and a review of the literature that cumulatively aid in determining the environmental conditions that existed in the past for specific geologic units.