Summary: Euhedra of weddellite have been recognized in modern, unconsolidated sediments collected from depths of water not exceeding one fathom, along the south-east coast of Florida. For weddellite, the following data have been deter-mined: crystals simple with r {01} accompanied by a {010} in some cases; goniometric axial ratio is a:c = 1:0·593 (meas.), 1:0·5938 (calc.); a₀ 12·360 Å, c₀ = 7·340 Å; space group I4/m, I4 or I4¯; α 1·529, γ = 1·544, δ = 0·015, uniaxial, positive; d_22°C = 1·941. Heat treatment of weddellite led to development of whewellite, calcite, and calcium oxide in turn as higher temperatures were employed; fully indexed X-ray diffraction powder data are given for weddellite, in addition to d-spacings and intensities for whewellite.

It is suggested that weddellite developed in the calcareous Florida sediments under conditions of storage over a two-year period, and ahnost certainly was not a constituent of those sediments at the time of collection. This raises the question whether weddellite was present in the Weddell Sea material at the actual time they were recovered by members of the Scotia Expedition.