Pierre Teilhard de Chardin came up in a conversation about mystical Christianity and panentheism, and in searching for selections of his writings online, I found that in fact many of his works are available online in their entirety, as are some collections of selections and excerpts. A list follows below, but you may want to start with a selection of quotes to whet your appetite.
The Future of Mankind
(also at the Internet Archive as The Future of Man)
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