Blackboard ‘chalk’ are produced especially for use with blackboards in white and also in various colours. White chalk sticks are made mainly from calcium carbonate derived from mineral chalk rock or limestone, while colored or pastel chalks are made from calcium sulfate in its dihydrate form, CaSO·2HO, derived from gypsum. Chalk sticks containing calcium carbonate typically contain 40–60% of CaCO (calcite). As compared to whiteboards, blackboards still have a variety of advantages: On the other hand, chalk produces dust, the amount depending on the quality of chalk used. Some people find this uncomfortable or may be allergic to it, and according
What Are Little Girls Made Of? Handlen of "The A.V. Club" gave the episode a 'B+' rating, noting that the "repetitive plotting" took away any real sense of threat and that without Spock or McCoy to play off, Kirk's character is less interesting. What Are Little Girls Made Of? "What Are Little Girls Made Of?" is the seventh episode of the of the American science fiction television series, "". Written by Robert Bloch and directed by James Goldstone, it first aired on October 20, 1966. The first episode of the series to be repeated on NBC, the title of the episode is taken from the fourth