Biogenic sands are widespread on the planet coasts and in shallow waters (mainly in low latitudes). This type of sediments is composed of pieces the skeletal remains of plants and animals such as clams, sea snails, foraminifera, algae, corals, echinoids, sponges, etc. This biogenic material consists mainly of calcium carbonate. Determination of organic matter in these sands is associated with a number of methodological difficulties, especially if carbonates constitute the main fraction. There are two main approaches for the determination of organic carbon on marine sediments, namely (1) chemical oxidation of organic matter and (2) high-temperature combustion. Both of these approaches are affected by carbonate harmful influence. Approach (1) is completely unsuitable due to the fact that carbonates react with an oxidizing agent (sulphuric acid and potassium dichromate). Approach (2) is influenced by oxidizing carbonates at high temperature. The Loss-On-Ignition method relates to approach (2). In the ‗normal‘ case the sample of sediments is treated in a muffle furnace for certain time (usually 1.5-6 hours) at high temperature (most commonly 450-950o C). The difference between the initial and final sample weights is converted to organic carbon units. For slightly calcified sediments is recommended to eliminate carbonates by hydrochloric acid with following rinsing, filtering and drying to remove reaction products. But the predominance of carbonates in biogenic sands makes this recommendation difficult to implement. Additionally, flushing and filtration can result in the loss of some of the water-soluble organic matter The reaction between calcium carbonates and hydrochloric acid leads to the formation of calcium chloride which is highly hygroscopic. We propose the scheme of temperature-controlled weightings after carbonates and hydrochloric acid reaction. The fact is that calcium chloride hydrate contains different amounts of water depending on the temperature. We propose to control this factor by using pure calcium chloride as a ‗blank‘. This blank should be processed together with the sample after HCl treatment in all stages. There are following stages: drying, combustion, cooling, and weighting. Weighing of the sample and blank should be carried out immediately after each other after stabilization of the selected temperature.