Fig. 4: Box plots showing the distribution of mole% MgCO3 values among Pennsylvanian echinoderms from marine facies (ref.15), coal-ball echinoderms and HMC cement from the Dalton and Calhoun coals.
From: A marine origin of coal balls in the Midland and Illinois basins, USA
a Echinoderms from Pennsylvanian marine facies (ref. 15), Dalton coal, and Calhoun Coal. b Dalton echinoderms and HMC cements from mixed and plant-only coal balls. c Calhoun echinoderms and HMC cements from mixed and plant-only coal balls. For all box plots, the boxes extend from the upper and lower quartiles (interquartile range, Q3 to Q1), the horizontal solid black line is the median. Whiskers extend from boxes out to 1.5 times the interquartile range. Data points are shown in small, black circles. Any data past the ends of the whiskers are outliers and shown as large, black circles.
