Using micro-laser Raman spectroscopy, it is shown for the first time that calc-agglutinated foraminifera use one of either of two polymorphs of CaCO3, namely calcite or aragonite, as the mineralized cement to bind together the detrital grains. With the exception of one optical microscopy study, previous studies have used indirect methods, such as X-ray diffraction of whole tests or energy dispersive X-ray analysis, to infer the cement composition and mineralogy. All records to date have suggested that the mineral phase is calcite. We confirm this for Spirorutilis wrightii and provide the first record of the use of aragonite as biomineralized cement in the agglutinated foraminiferan Texrularia crenara. Previously aragonite was known only from the hyaline walls of the suborder Robertinina. This discovery has potential implications for the classification of the group.

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