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Close up of piece of white chalk on black slate. Blackboard chalk manufacturers now may use mineral chalk, other mineral sources of calcium carbonate, or the mineral gypsum (calcium sulfate). 素材庫相片
![Close up of piece of white chalk on black slate. Blackboard chalk manufacturers now may use mineral chalk, other mineral sources of calcium carbonate, or the mineral gypsum (calcium sulfate). Stock Photo Close up of piece of white chalk on black slate. Blackboard chalk manufacturers now may use mineral chalk, other mineral sources of calcium carbonate, or the mineral gypsum (calcium sulfate). Stock Photo](https://as1.ftcdn.net/v2/jpg/04/00/62/26/500_F_400622686_XQEn8w8K7c8XpiK8NBXpQKEEhPAtYi8v.jpg)
Close up of piece of white chalk on black slate. Blackboard chalk manufacturers now may use mineral chalk, other mineral sources of calcium carbonate, or the mineral gypsum (calcium sulfate). Stock Photo
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Construction of Waste Chalk Powder into mpg-C3N4-CaSO4 as an Efficient Photocatalyst for Dye Degradation under UV–Vis Light and Sunlight | Langmuir
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![Gypsum isolated on black. Sulfate mineral composed of calcium sulphate, used as plaster and blackboard chalk Stock Photo - Alamy Gypsum isolated on black. Sulfate mineral composed of calcium sulphate, used as plaster and blackboard chalk Stock Photo - Alamy](https://c8.alamy.com/comp/EKH2G7/gypsum-isolated-on-black-sulfate-mineral-composed-of-calcium-sulphate-EKH2G7.jpg)
Gypsum isolated on black. Sulfate mineral composed of calcium sulphate, used as plaster and blackboard chalk Stock Photo - Alamy
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Colored Chalks Tote for Chalkboard, Assorted Colors - China Colored Chalks, Cheap Chalk | Made-in-China.com
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