Calcium carbonate

Calcium oxide (99.9%) and nanosized calcium
oxide (<160 nm, 98%) were purchased from Sigma-Aldrich Inc. and
used as received. Calcium carbonate (99.999%) was used as received
from Mallinckrodt. Calcium hydroxide (99%) and hydrochloric acid (36
wt %) were obtained from Fischer Chemicals, and absolute ethanol (200
proof) was acquired from Decon Labs Inc. Dissolved acetylene and industrial
nitrogen were sourced from Airgas. For conductivity measurements,
gold foil (99.9%) was obtained from Aesar and aluminum foil from Reynolds.

Data for 20 calcite standards and 1 dolomite standard are reported (Table 2). These include ETH‐1, ETH‐2, ETH‐3, ETH‐4, IAEA‐C1, IAEA‐C2, and MERCK, as described in Bernasconi et al,¹⁷ and NBS‐19, SRM 88B (dolomite), Mallinckrodt Calcium Carbonate, 102‐GC‐AZ01, Carmel Chalk, Carrara Marble, CMTile (another homogenized Carrara Marble), Spel 2‐8‐E, TV01, TV03, and VeinStrom. Carbonate standards obtained from the California Institute of Technology (CIT) and China University of Geosciences (CUG) include Coral Std, ISTB‐1, TB‐1, and TB‐2.⁴² These carbonates span a range of δ₄₇ that is more than 30‰ and ~0.5‰ in Δ₄₇. Raw data and analyzed results are provided in the supporting information.