Potassium, rubidium, and caesium react with graphite; their atoms are intercalated between the hexagonal graphite layers, forming graphite intercalation compounds of formulae MC60 (dark grey, almost black), MC48 (dark grey, almost black), MC36 (blue), MC24 (steel blue), and MC8 (bronze) (M = K, Rb, or Cs).
pətˈæsiəm, ɹuːbˈɪdiəm, ænd sˈiːsiəm ɹɪˈækt wɪð ɡɹˈæfaɪt; ðɛɹ ˈæɾəmz ɑːɹ ɪntˈɜːkɐlˌeɪɾᵻd bᵻtwˌiːn ðə hˈɛksɐɡənəl ɡɹˈæfaɪt lˈeɪɚz, fˈɔːɹmɪŋ ɡɹˈæfaɪt ɪntˌɜːkɐlˈeɪʃən kˈɑːmpaʊndz ʌv fˈɔːɹmjʊlˌiː ˌɛmsˈiː sˈɪksti dˈɑːɹk ɡɹˈeɪ, ˈɔːlmoʊst blˈæk, ˌɛmsˈiː fˈoːɹɾi ˈeɪt dˈɑːɹk ɡɹˈeɪ, ˈɔːlmoʊst blˈæk, ˌɛmsˈiː θˈɜːɾi sˈɪks blˈuː, ˌɛmsˈiː twˈɛnti fˈoːɹ stˈiːl blˈuː, ænd ˌɛmsˈiː ˈeɪt bɹˈɑːnz ˈɛm ˈiːkwəlz kˈeɪ, ˌɑːɹbˈiː, ɔːɹ sˌiːˈɛs.