What is a hard and strong rock with thin, flattened crystals packed tightly together?

what is a brittle rock that contains fine grains and layers with fossil remains?

Many organizations release indexes used to measure the development of the world's countries. as we learned in this lesson, these indexes measure many factors, from life expectancy to happiness. in your opinion, what are the three most important factors we can use to determine how developed a country might be? explain your answers in a few sentences.