Without actually holding and touching it, if it is indeed light weight, there's a good chance that it is jet. The streaks of brown could lead one to think it is a black tiger eye, however, jet did occasionally have some brown streaks visible in it.
Jet is actually Lignite coal and was very popular in the Victorian era as a "mourning" stone. Most jet beads that were used in rosaries and mourning jewelry were made of a fine French glass because it held up better -- jet is not particularly hard.
Lignite, in its sedimentary form, is actually brown, and is not a very efficient coal for heating. Some the harder, glassier forms (used for jet) are closer to black and glassy in appearance. It is light weight and easily carved or faceted. Be aware that some jet beads were mixed, or stabilized, with glue/resin to maintain its shape (much as some turquoise is today).
There is one thing you can try with your beads. Jet becomes electrically charged when rubbed with wool or silk. Try quickly rubbing the beads with wool or silk to see if you can get a static charge from it. Also, find a very discreet spot on one of the beads and touch a red hot needle to it. You should get the faint smell of burning coal (which many of us remember from our coal furnace days!). If you do get both reactions, you almost certainly have jet beads.
https://en.wikipedia.org/wiki/Jet_(lignite)
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“Let’s work the problem, people. Let's not make things worse by guessing.” -Gene Kranz, Mission Control Director (played by Ed Harris), Apollo 13
